Properties Of Single Neurons Research Articles

Functional properties of single neurons in the primate face primary somatosensory cortex. II. Relations with different directions of trained tongue protrusion

1. In previous papers we have presented evidence suggesting an important role for the face primary somatosensory cortex (SI) in the fine control of tongue movements. These findings, plus our earlier evidence that many neurons in face motor cortex (MI) may exhibit firing rates related to the direction of tongue protrusion, led us to test the hypothesis that variations in the direction of a tongue-protrusion movement would be associated with variations in the activity of different face SI neurons. 2. Two monkeys were trained to perform a tongue-protrusion task in each of three directions: the task transducer was positioned at 0 degrees, 30 degrees to the left, or 30 degrees to the right from the midsagittal plane. The latter two positions were termed asymmetrical tongue-protrusion task positions. Single-neuron activity was recorded from face SI during trials of the tongue-protrusion task at each of two or three of the above positions. In addition, the mechanoreceptive field (RF) was delineated for each neuron. 3. Directional relations were found in 25 (58%) of the 43 neurons studied; this included 20 neurons showing a significant direction-by-time interaction in firing rate, i.e., the change of firing rate from the pretrial period to the task period was significantly different between different directions, and 5 showing no direction-by-time interaction but a significant difference in firing rate between different directions of the tongue-protrusion task. 4. Of the 43 neurons investigated, 21 and 20 had a RF on the tongue and lips, respectively ("tongue RF" and "lip RF" neurons), and the remaining 2 received mechanosensitive afferent inputs from other orofacial regions. There was no significant difference in the incidence of directional sensitivity between the neurons with a tongue RF and those with a lip RF (12/21 and 11/20, respectively). 5. Eight of the 25 "directional" neurons were located in area 3b and 17 in area 1. There was no significant difference in the proportion of directional neurons between areas 3b and 1. 6. The increase in discharge frequency at the preferred direction was, on the average for the 25 directional neurons, 39% over the mean discharge frequency observed during the task period for all directions of the tongue-protrusion task. Eight directional neurons showed a significant increase in firing rate during the tongue-protrusion task up to 130 ms before the onset of genioglossus electromyographic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional properties of single neurons in the primate face primary somatosensory cortex. III. Modulation of responses to peripheral stimuli during trained orofacial motor behaviors

1. In previous papers we have demonstrated that most single neurons in the face primary somatosensory cortex (SI) alter their firing rate during a trained tongue-protrusion task and some also during a trained biting task. Although the data suggest that some of the task-related activity in face SI might conceivably come from reafferent inputs from moving orofacial structures, it is possible that orofacial inputs are modulated during the trained orofacial movements. This study was initiated to investigate the possible modulation of evoked orofacial somatosensory responses of face SI neurons during trained tongue-protrusion and biting tasks. 2. Two monkeys were trained to perform a tongue-protrusion and a biting task and to accept stimulation applied to the facial skin or the lingual nerve during the tasks. For SI neurons with a tongue mechanoreceptive field (RF), electrical stimulation was applied to the lingual nerve to elicit neuronal activity; for SI neurons with a RF at the other locations, electrical or mechanical stimulation was applied to the RF to elicit neuronal activity. Modulation of neuronal activity evoked by low-threshold stimulation of the RF was tested, during the tongue-protrusion and/or biting tasks, in 44 face SI neurons and an additional 3 forelimb SI neurons with a palm RF (palm RF neurons). The 44 face SI neurons included 13 with a tongue RF (tongue RF neurons), 29 with a lip RF (lip RF neurons), and 2 with a lateral face RF (face RF neurons). 3. For face SI neurons tested during both force dynamic and holding phases of the task period, the evoked activity (i.e., the number of evoked spikes in 50 ms after the onset of stimulation) was decreased in at least one of the two phases for the majority (90%) of 31 neurons studied during the tongue-protrusion task and 61% of 23 studied during the biting task. The proportion of neurons modulated during the tongue-protrusion task was significantly higher than that during the biting task. For the 18 face SI tested during both tasks, a decrease in evoked activity occurred in 10 lip RF neurons for both tasks and in the remaining 5 lip RF and 3 tongue RF neurons for the tongue-protrusion task only. No neurons tested showed a clear facilitation of evoked activity during the task period of either task.(ABSTRACT TRUNCATED AT 400 WORDS)

Visual response properties of single neurons in the temporal pole of behaving monkeys.

1. The responses of single neurons in the anterior part of the temporal cortex in monkeys, mainly the temporopolar cortex, area 36, and the most anterior part of area TE of von Bonin and Bailey (1947) (these areas were designated here as the temporal pole), were examined during the performance of a visual recognition memory task. The visual stimulus (sample stimulus) was presented when the monkey pressed a lever. The same sample stimulus was presented one to four times and, thereafter, a new stimulus was presented. The monkeys were trained to discriminate the new stimulus from the sample stimulus and to release the lever in response to the new stimulus. We used colored photographs of natural objects (human faces, monkeys, foods, and non-food objects) as complex visual stimuli or computer-generated two-dimensional shapes (a red square, a green circle, etc.) as simple visual stimuli. 2. In total, the activity of 311 neurons was recorded, and 225 of these responded to at least one visual stimulus. All visually responsive neurons were located in the ventral part of the temporal pole including the banks of the superior temporal sulcus. 3. The relationship between the monkey's eye movements and visual responses was investigated. Visual response properties, such as the number of spikes, onset latency, and response duration, were stable regardless of the monkey's eye positions and movements if the eyes were directed to the display. We also examined the receptive field property of neurons (n = 3). The neurons tested in the temporal pole tended to have a large receptive field (24 x 24 degrees). 4. The neurons tended to respond to different stimuli in different magnitudes. In each case, the maximal responses were elicited by complex, colored photographs, whereas simple, two-dimensional colored shapes elicited little or no responses. In 21% of the cases (47/225), the magnitude of the maximal response was significantly larger than for any of the other responses. 5. An achromatic version of the stimulus that induced the maximal response was tested in 53 neurons. About 80% of the neurons (41/53) responded to the achromatic stimulus at a magnitude that was not significantly different from the response to the original stimulus. In 12 neurons, the removal of color did significantly decrease the magnitude of the response. When other colors were tested, 3 of 9 neurons were found to code for color. 6. In 21 of these 53 neurons, a portion (the left-, right-, upper-, or lower-half) of the stimulus was also tested.(ABSTRACT TRUNCATED AT 400 WORDS)

Response properties of single units in areas of rat auditory thalamus that project to the amygdala. I. Acoustic discharge patterns and frequency receptive fields.

Projections from the auditory thalamus to the amygdala have been implicated in the processing of the emotional significance of auditory stimuli. In order to further our understanding of the contribution of thalamoamygdala projections to auditory emotional processing, acoustic response properties of single neurons were examined in the auditory thalamus of chloral hydrate-anesthetized rats. The emphasis was on the medial division of the medial geniculate body (MGm), the suprageniculate nucleus (SG), and the posterior intralaminar nucleus (PIN), thalamic areas that receive inputs from the inferior colliculus and project to the lateral nucleus of the amygdala (AL). For comparison, recordings were also made from the specific thalamocortical relay nucleus, the ventral division of the medial geniculate body (MGv). Responses latencies were not statistically different in MGv, MGm, PIN, and SG, but were longer in the posterior thalamic region (PO). Overall, frequency tuning functions were narrower in MGv than in the other areas but many cells in MGm were as narrowly tuned as cells in MGv. There was some organization of MGv, with low frequencies represented dorsally and high frequencies ventrally. A similar but considerably weaker organization was observed in MGm. While the full range of frequencies tested (1-30 kHz) was represented in MGv, cells in MGm, PIN, and SG tended to respond best to higher frequencies (16-30 kHz). Thresholds were higher in PIN than in MGv (other areas did not differ from MGv). Nevertheless, across the various areas, the breadth of tuning was inversely related to threshold, such that more narrowly tuned cells tended to have lower thresholds. Many of the response properties observed in MGm, PIN, and SG correspond with properties found in AL neurons and thus add support to the notion that auditory responses in AL reflect thalamoamygdala transmission.

Ionic mechanisms for intrinsic slow oscillations in thalamic relay neurons

The oscillatory properties of single thalamocortical neurons were investigated by using a Hodgkin-Huxley-like model that included Ca2+ diffusion, the low-threshold Ca2+ current (lT) and the hyperpolarization-activated inward current (lh). lh was modeled by double activation kinetics regulated by intracellular Ca2+. The model exhibited waxing and waning oscillations consisting of 1-25-s bursts of slow oscillations (3.5-4 Hz) separated by long silent periods (4-20 s). During the oscillatory phase, the entry of Ca2+ progressively shifted the activation function of lh, terminating the oscillations. A similar type of waxing and waning oscillation was also observed, in the absence of Ca2+ regulation of lh, from the combination of lT, lh, and a slow K+ current. Singular approximation showed that for both models, the activation variables of lh controlled the dynamics of thalamocortical cells. Dynamical analysis of the system in a phase plane diagram showed that waxing and waning oscillations arose when lh entrained the system alternately between stationary and oscillating branches.

Response properties of neurons in temporal cortical visual areas of infant monkeys.

1. Inferior temporal cortex (IT) is a "high-order" region of primate temporal visual cortex implicated in visual pattern perception and recognition. To gain some insight into the development of this area, we compared the properties of single neurons in IT in infant monkeys ranging from 5 wk to 7 mo of age with those of neurons in IT in adult animals. Both anesthetized and awake behaving paradigms were used. 2. In immobilized infant monkeys under nitrous oxide anesthesia, the incidence of visually responsive cells was markedly less than in adult monkeys studied under similar conditions. In infants 4-7 mo of age, only half of IT neurons studied were visually responsive, compared with > 80% in adult monkeys. In monkeys < 4 mo old, even fewer (< 10%) could be visually driven. "Habituation" of IT cells to repeated stimulus presentation appeared more pronounced in infant monkeys under nitrous oxide anesthesia than in adult animals. 3. IT cells in the anesthetized infant monkeys that did respond showed receptive field properties similar to those of responsive adult IT neurons studied under similar conditions. Two thirds of the receptive fields plotted in the anesthetized 4 to 7-mo-old group were bilateral, and median field size did not differ between the infants and comparable adult groups, being approximately 20 degrees on a side in each case. 4. In contrast to the results obtained under anesthesia, most IT cells in alert infant monkeys 5 wk-7 mo of age (80%) were responsive to visual stimuli, and this incidence of visually responsive IT neurons did not differ from that obtained in awake adult macaques. However, response magnitude, measured as spikes per second above baseline rate, was significantly lower in the infant alert sample than in the adult control (5.2 vs. 12.6 spikes/s, mean +/- SE, deviation from spontaneous rate, respectively). 5. In addition to having lower magnitudes of visual response, IT cells in the awake infants also tended to have longer and more variable latencies. The overall mean for the infant cells was 196 ms, compared with an overall mean of 140 ms for IT neurons in the alert control adult. 6. Although the magnitude of response of neurons in alert infant IT cortex was lower overall, the incidence and features of stimulus selectivity shown by alert infant IT neurons were strikingly similar to those of IT cells of both anesthetized and unanesthetized adult monkeys.(ABSTRACT TRUNCATED AT 400 WORDS)

Sensory tuning beyond the sensory system: an initial analysis of auditory response properties of neurons in the lateral amygdaloid nucleus and overlying areas of the striatum

The lateral amygdaloid nucleus (AL) is anatomically connected with sensory processing structures in the thalamus and cortex and is believed to be critically involved in emotional processing by virtue of these connections. In order to understand further how auditory projections to AL contribute to emotional processing, acoustic response properties of single AL neurons were characterized in rats. Recordings were also made in the posterior striatum dorsal to AL. Many cells in AL and the striatum could be driven by broad-band auditory stimulation with white noise or clicks. Initial onset latencies were typically between 12 and 25 msec. Most cells also had later responses (60-150 msec), and a few only had late responses. In frequency receptive field tests, different classes of cells were identified. One group had relatively clear frequency preferences. Thresholds for these relatively tuned cells tended to be somewhat higher in AL than in the striatum. Frequency preferences for AL cells were always above 10 kHz. Although most striatal cells had preferences for frequencies above 10 kHz, some cells were found with frequencies below 10 kHz as well. A second group of acoustically responsive neurons, much more common in AL than in the striatum, showed no frequency specificity (untuned cells). These responded to a wide range of frequencies, even at intensities near threshold. A third group, found mainly in AL (approximately 60% of the total population of cells examined in AL), exhibited rapid habituation to auditory stimuli. These tended to have high thresholds (80-100 dB). Because these cells habituated so quickly, frequency specificity could not be determined. Responses in AL and the striatum were compared with responses in the "specific" auditory relay nucleus of the thalamus, the ventral division of the medial geniculate body, where cells had shorter onset latencies, narrower tuning functions, and lower-intensity thresholds than cells in AL and striatal areas. These findings show that cells in AL exhibit a wide range of auditory tuning properties and suggest that information processing in the amygdala might be fruitfully studied as a direct extension of processing in sensory afferent structures.

Development of tone response thresholds, latencies and tuning in the mouse inferior colliculus

The development of tone response thresholds, latencies and tuning of neurons in the inferior colliculus (IC) of the mouse has been investigated between postnatal days 10 (first responses) and 20. As in adults, response thresholds of neurons are lowest in the center of the IC compared with other areas right from the beginning of responsiveness at day 10. Thresholds decrease rapidly until at days 16–20 (depending on the characteristics frequency of the neurons) adult levels are reached. Response latencies decrease rapidly to adult levels at days 16–18. Broad frequency tuning curves can be measured at days 10 and 11. From day 12 onwards, tuning curve shapes differentiate and adult diversity occurs which indicates presence of inhibition and summation in the pathway to or within the IC at that early age. The tip lengths of the tuning curves increase faster than the sharpness of the tips ( Q 10dBvalues). The developmental courses of the measured parameters are expressed by power functions. The time constants of these functions are used in the discussion of processes underlying the functional maturation in the auditory system of the mouse. The general course of the development of all the here investigated response properties of single neurons in the IC, except tuning curve shape, appears to be determined by maturation at or peripheral to the cochlear level.

Functional properties of single neurons in the face primary motor cortex of the primate. I. Input and output features of tongue motor cortex.

1. We have recently demonstrated that reversible, cooling-induced inactivation of the face motor cortex results in a severe impairment in the ability of monkeys (Macaca fascicularis) to perform a tongue-protrusion task but produces only relatively minor effects on the performance of a biting task by the same monkeys. To establish a neuronal correlate for these different behavioral relations, the present study has detailed the afferent input and intracortical microstimulation (ICMS)-defined output features of a population of face motor cortical neurons, and in a subsequent study we have documented the activities of the same population of neurons during the performance of the tongue-protrusion and biting tasks. 2. Of the 231 single neurons recorded within the face motor cortex, 163 were located at sites from which ICMS (less than or equal to 20 microA) could evoke tongue movements (i.e., "tongue-MI" sites) at the lowest threshold for eliciting orofacial movements. The remainder were located at sites from which ICMS evoked jaw movements ("jaw-MI" sites), face movements ("face-MI" sites), or at a few sites, tongue movements and, at the same threshold intensity, either a jaw movement or a facial movement. 3. We confirmed the general organizational features of the face motor cortex that have been defined in previous studies, but we documented in detail the organizational features for tongue-MI. Thus we found that tongue movements were well represented, whereas jaw-closing movements were poorly represented; the representations for face, jaw, and tongue movements were overlapped; the same ICMS-evoked tongue movement could be multiply represented within tongue-MI; tongue-MI was characterized by a prominent input from superficial mechanosensory afferents, whereas there was little evidence for deep input; a close spatial match was found between ICMS-defined motor output and somatosensory afferent input for tongue-MI. 4. A variety of tongue movements could be evoked by ICMS at tongue-MI sites and were categorized into protrusion, retrusion, laterally directed, and other types of tongue movement. Low-threshold (i.e., less than or equal to 5 microA) ICMS-defined tongue-MI sites, which were considered to represent "efferent zones" projecting relatively directly to motoneurons, were reconstructed three dimensionally to provide insights into the spatial organization of tongue-MI. Examples of each of the four low-threshold efferent-zone categories were usually found throughout the ICMS-defined tongue-MI without any apparent preferential distribution. Furthermore, different low-threshold efferent-zone categories had close spatial relationships to each other in cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional properties of single neurons in the face primary motor cortex of the primate. III. Relations with different directions of trained tongue protrusion.

1. In previous papers we presented evidence pointing to an important role for face motor cortex in the control of tongue movements. Intracortical microstimulation (ICMS) at many sites within face motor cortex evoked different types of tongue movement, and many neurons at these "tongue-MI" sites received intraoral mechanosensitive afferent input, and their activity was related to a tongue-protrusion task performed by a monkey. In view of the synergistic action of the various tongue muscles during tongue movement, we hypothesized that these different tongue-MI sites are recruited to effect the appropriate change in tongue shape and position during a tongue-protrusion movement. A prediction from this hypothesis is that variations in the direction of a tongue-protrusion movement should be associated with variations in the activities within the different tongue-MI efferent zones. Differences in efferent-zone activity should be reflected in differences in the firing rates of neurons that are located at these tongue-MI sites. 2. We trained two monkeys to perform a tongue-protrusion task at each of three directions. The tongue-protrusion task transducer was positioned at 0 degrees (Ts), 30 degrees to the left (Tlt), or 30 degrees to the right (Trt) from the midsagittal plane; the latter two positions were termed asymmetric tongue-protrusion task positions. Single neurons were recorded from tongue-MI during trials of tongue-protrusion task at each of two or three of the above positions. Some of the neurons were also studied during a biting task. In addition, neurons were tested for possible mechanosensitive afferent input. 3. Of the 66 neurons studied, 31 (45%) exhibited directional relations; that is, the change in firing rate between the pretrial period (PTP) and the task period for the tongue-protrusion task was significantly different for each neuron depending on the direction in which the activity of the neuron was studied. 4. The "directional" neurons exhibited a single preferred direction of firing in that the mean firing rate during one direction of tongue-protrusion task was significantly greater than for any other direction. Of the 20 neurons studied at all three directions of tongue-protrusion task, the mean firing rate of each of 18 was highest at one of the asymmetric positions, and 12 of these 18 neurons exhibited a monotonic decrease in absolute firing frequency from one asymmetric task direction to the other. 5. Thirteen of the neurons were also studied while the monkey performed the biting task. Most tongue-MI directional neurons were not related to the biting task.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional properties of single neurons in the face primary motor cortex of the primate. II. Relations with trained orofacial motor behavior.

1. The previous paper has described in detail the input and output features of single neurons located at sites within primate face motor cortex from which intracortical microstimulation (ICMS, less than or equal to 20 microA) evoked tongue movements at the lowest threshold ("tongue-MI" sites); for comparative purposes, we also reported on the input and output features of a smaller number of neurons recorded at sites from which ICMS could evoke jaw movements ("jaw-MI" sites), facial movements ("face-MI" sites), or, at a few sites, tongue movements and, at the same threshold intensity, either a jaw movement or a facial movement. 2. Our findings of an extensive and diverse representation of sites within face motor cortex of monkeys for the generation of elemental components of tongue movement, and the relatively few sites from which jaw-closing movements could be evoked, were consistent with our recent observations that reversible, cooling-induced inactivation of the face motor cortex severely impaired the performance by monkeys of a tongue-protrusion task but had only relatively minor effects on the performance of a biting task. In an attempt to establish a neuronal correlate for these different behavioral relations, the present study has documented the task-related activities of those single neurons that were characterized in the previous paper in terms of afferent input and ICMS-defined output features. 3. Each task required the development and maintenance by each monkey of a fixed force level for a minimum period of time to obtain a fruit-juice reward. During one or both of these tasks, we characterized the activities of 231 single face motor cortical neurons that were located at the above-mentioned ICMS-defined sites. Neurons were said to be related to a particular task if they showed statistically significant differences in firing rates during the task in comparison with a control pretrial period (PTP). 4. In tongue-MI, there was a significantly higher proportion of neurons (63% of 156 neurons tested) that were related to the tongue-protrusion task than to the biting task (15% of 65). However, in jaw-MI the proportion of neurons that were biting task-related (63% of 19) was significantly higher than the proportion related to the tongue-protrusion task (11% of 9); the proportion of biting task-related neurons at ICMS-defined jaw-closing sites was also higher than that at jaw-opening sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Convergent inputs to single neurons in two different subdivisions of somatosensory forepaw digit cortex of the raccoon

The aim of this study was to compare the physiological properties of single neurons in the glabrous (G) and heterogeneous (H) subdivisions of primary somatosensory digit 3 cortex of adult raccoons. Extracellular recordings were obtained from 50 G neurons whose receptive fields (RFs) were confined to the glabrous skin of a digit, and 41 H neurons whose RFs were located on hairy skin, claws, or mixtures of skin types. Both electrical and mechanical stimulation of the digits were used to assess excitatory neuronal responsiveness. The two sets of neurons, which had nearly identical depth distributions, differed considerably in their input convergence: (i) the percentage of neurons (% N) responding to electrical or mechanical stimulation of each off-focus digit and (ii) the number of digits from which individual cells could be driven were significantly greater for H neurons. Those G and H cells which could be excited by off-focus inputs were examined for probability of response ( P), number of spikes per response ( S R ), and latency of response ( L) to digit stimulation. Surprisingly, for input from any one digit, there were no significant differences in these response properties between the two sets of neurons. However, inputs from different (on-focus versus off-focus) digits varied significantly and revealed patterns of response properties that were qualitatively similar for both G and H neurons. Specifically, % N and P decreased while L increased symmetrically with distance of each off-focus digit from the central on-focus digit 3, reflecting corresponding variations in the synaptic accessibility and conduction time of off-focus excitatory inputs. In contrast, S R values were very similar for all digits, suggesting that the synaptic strength of off-focus inputs is regulated independently of accessibility. Finally, preliminary findings indicated that denervation of the third digit caused a decrease in off-focus response latencies, while the normal latency profile across digits was retained. This suggests that the previously existing pattern of off-focus inputs to G and H neurons provides a template for denervation-induced cortical reorganization, whereby the synaptic efficacy of off-focus inputs is increased by disinhibition or facilitation.

Posterior cingulate cortex: sensory and oculomotor properties of single neurons in behaving cat.

The posterior cingulate cortex of the cat is strongly linked to cortical areas with sensory and oculomotor functions. We have now recorded from feline posterior cingulate neurons in order to determine whether they are active in conjunction with sensory events and eye movements. The results described here are based on monitoring the electrical activity of 195 single neurons in the posterior cingulate cortex of three cats equipped with surgically implanted scleral search coils and trained to fixate visual targets. Posterior cingulate neurons carry tonic orbital position signals and are phasically active in conjunction with saccadic eye movements. Activity related to eye movements and gaze is attenuated but not abolished by the elimination of visual feedback. Posterior cingulate neurons also are responsive to visual, auditory, and somatosensory stimulation. Systematic testing with visual stimuli revealed that responses are sharply reduced due to refractoriness at rates of stimulation greater than a few per second. These results conform to the theory that posterior cingulate cortex is involved in processes underlying visuospatial cognition.

Setting complex tasks to single units in the avian auditory forebrain. II: Do we really need natural stimuli to describe neuronal response characteristics?

The response characteristic of auditory forebrain neurons in the European starling was established both with artificial stimuli (AS) and a conspecific territorial song as a natural stimulus (NS1). Applying experimenter-centred statistical methods for response detection and for scaling response strength, and spike-triggered analyses for the delimitation of the key sound parameters (spectrotemporal receptive field STRF, Aertsen et al. 1980) the study aimed at disclosing differences in the processing of the two stimulus classes, AS and NS. With the STRF as reference, we find congruence 1. (1) in the best frequency with those determined under sweep and bandpass noise stimulation, 2. (2) in response latency, and 3. (3) in response-intensity dependence, further similarity in the overall frequency characteristic. Partitioning the song into 42 acoustically defined segments allowed to further delimit the response criteria under natural stimulation. They are easily understood from the AS response characteristics: 1. (1) In the neuronal sample as a whole, long segments are more effective than short and, among the short, loud segments are more effective than faint; 2. (2) Units showing their best excitatory response to AS in a certain frequency band are most probably excited by segments with a high proportion of their power concentrated upon or near this band; (3) Units with a slow (build-up) AS response react to a lower number of song segments than those dynamically following AS transients. Our data give no hint towards adaptive, feature detection properties of single neurons in field L. Instead, these neurons appear to base their response solely on the short-time spectrotemporal structure of the stimulus, irrespective of its natural or artificial origin.

Red nucleus: role in motor control

Experimental reports in the past year have provided a better understanding of the motor functions of excitatory and inhibitory neurotransmitters in the red nucleus, and of the sensorimotor properties of single rubral neurons. These data fit well within the framework of a neural network model of the rubrocerebellar system.

Sound frequency and binaural response properties of single neurons in rat inferior colliculus

Sound frequency and binaural response properties were determined for single neurons in the rat's inferior colliculus. Nerve cell responses in the central nucleus of the inferior colliculus were narrowly tuned and had clearly defined characteristic frequencies (CF). The central nucleus was tonotopically organized with low frequencies represented dorsolaterally and high frequencies ventromedially from 0.87 to 45 kHz. Sharpness of tuning, as indicated by Q 10, covered a wide range of values for neurons with the same CF, but the maximum Q 10 at each frequency increased monotonically with CF. Maximum Q 10s were larger than previously reported for auditory cortex at the same CF. Binaural responses were classified as either suppression, summation or mixed. Most of the units encountered exhibited binaural suppression but there were substantial numbers of both summation and mixed responses. Each major binaural response type was distributed broadly across sound frequencies within the rat's hearing range. Binaural suppression responses were most numerous at high frequencies and summation responses at low frequencies. The binaural response types, their relative proportions and their distribution by CF were similar for neurons in the central nucleus of inferior colliculus and primary auditory cortex of the albino rat.

Auditory Pontine Grey: Connections and Response Properties in the Horseshoe Bat.

This study investigates the role of the pontine grey as a link between the auditory system and the cerebellum in the bat, Rhinolophus rouxi. We recorded response properties of single neurons in the pontine grey and, in the same preparation, injected wheat germ agglutinin - horseradish peroxidase (WGA - HRP) in areas responsive to sound. Thus the functional evidence was correlated with retrograde and anterograde transport. The main results are: (i) all auditory neurons in the pontine grey are tuned within one of two harmonically related frequency ranges of the echolocation call. The upper range corresponds to the constant frequency and frequency modulated components of the second harmonic, but the lower range corresponds only to the frequency modulated component of the first harmonic. There is no systematic tonotopic organization; (ii) discharge patterns are extremely variable, latencies cover a wide range, and about half of the neurons are binaurally responsive with excitation from both ears; (iii) most pontine auditory neurons respond preferentially to frequency modulated stimuli; (iv) there is massive input to the pontine grey from the central nucleus of the inferior colliculus; (v) cortical input to the pontine grey does not originate in tonotopically organized auditory cortex. The input is from a dorsal belt area that is specialized for processing combinations of sounds with specific frequency ratios and delays; (vi) projections from the auditory region of the pontine grey are widespread within the cerebellar cortex. The data suggest that the pontine grey transmits to the cerebellum information contained in specific components of the bat's biosonar signal.

Acoustic signaling in teleost fishes: Model systems for vertebrate vocalization

Teleost fishes can vocalize by contracting striated muscles attached to the lateral walls of their swimbladder. The rhythmic, oscillatory‐like, firing properties of a brain‐stem sonic motor circuit determine the fundamental frequency of the acoustic signals. In the midshipman Porichthys notatus only large, nest‐building, egg‐guarding males generate long duration (up to 1 h) “hums” that attract females to the nests. Females, and smaller, “sneak‐spawning” males, do not hum. Behavorial sex differences in sound production are correlated with: (a) the soma‐dendritic dimensions and discharge frequency of individual sonic motoneurons and their presynaptic pacemaker neurons, (b) the functional architecture of sonic muscle fibers and myofibrils, and (c) the density of neuromodulator inputs to the sonic motor nucleus. The sonic motor circuit can serve as a “simple” model system for a detailed analysis of the synaptic and electro‐responsive properties of single neurons controlling the generation of sex‐ and species‐typical acoustic communication signals. The collaboration of Harriet Baker, Robert Baker, Richard Brantley, and Margaret Marchaterre is acknowledged. [Work supported by NSF, NIH, and Hatch Grants.]

Response properties of nociceptive and non-nociceptive neurons in the rat's trigeminal subnucleus caudalis (medullary dorsal horn) related to cutaneous and deep craniofacial afferent stimulation and modulation by diffuse noxious inhibitory controls

An electrophysiological study was carried out in anesthetized rats to characterize the properties of single neurons in trigeminal (V) subnucleus caudalis. Each neuron was functionally classified in terms of its cutaneous mechanoreceptive field properties as low-threshold mechanoreceptive (LTM), wide dynamic range (WDR) or nociceptive-specific (NS), and its responsiveness was also tested to electrical stimulation of hypoglossal (XII) nerve muscle afferents. Some neurons were also tested with noxious stimulation of the tail or forepaw for the presence of diffuse noxious inhibitory controls (DNIC) of evoked responses. A mechanoreceptive field localized to the ipsilateral orofacial region was a feature of all the neurons which were located in laminae I-VI; the LTM neurons predominated in laminae III/IV whereas the nociceptive (WDR, NS) were located in the superficial and especially deeper laminae of caudalis. The majority of the WDR and NS neurons were also activated by noxious heating as well as by noxious mechanical and electrical stimulation of their orofacial mechanoreceptive field, and in contrast to our previous studies in cats, most of these caudalis nociceptive neurons received C fiber as well as A fiber cutaneous afferent inputs. In contrast to the LTM neurons, but consistent with our previous data in cats, many of the nociceptive neurons also received convergent excitatory inputs from XII muscle afferents, and the stimulus-response functions of the WDR neurons indicated that they were capable of coding the intensity of A and C fiber craniofacial muscle afferent inputs as well as those from cutaneous afferents. The study has also documented for the first time that muscle afferent-evoked responses as well as those evoked by cutaneous afferent inputs to nociceptive neurons are subject to DNIC. These findings indicate that subnucleus caudalis plays an important role in the transmission of superficial and deep nociceptive information from the craniofacial region of the rat, and also reveal that responses of the nociceptive neurons evoked by deep as well as superficial afferent inputs can be powerfully modulated by other nociceptive influences originating from widespread parts of the body.

Properties of single neurons in the cat midsuprasylvian gyrus

Responses of cells in the midsuprasylvian gyrus (MSSG) of cats were investigated following electrical stimulation of the central lateral nucleus (CL) of the thalamus and tooth pulp, low-threshold cutaneous or visual afferents. Electrical stimulation in CL induced excitation in many cells located in cortical areas 5 and 7. Cells in these areas also received input from somato-sensory and visual afferents. Cells in MSSG showed a wide convergence from tooth pulp, low-threshold cutaneous afferents and from the CL. The majority of wide convergent cells in area 5 were found in layers IV and V, while cells excited by CL and tooth pulp were found in layers II and III. Similarities were found between CL and tooth pulp evoked responses with regard to the excitation-inhibition pattern. The excitation evoked from CL and tooth pulp was less often followed by a hyperpolarizing potential compared to that seen after low-threshold lip, paw and visual afferent stimulation. Stimulation sites in the lateral parts of CL-evoked responses with the shortest latencies in area 5. In this part of the cortex, short latency synaptic potentials were found in cells in superficial layers. In the same area, synaptic potentials of short latency were also evoked by electrical stimulation of tooth pulp, lip and paw. Light-flash stimulation evoked responses with the shortest latencies in area 7. The results of this study demonstrate that putative nociceptive information reaches the parietal association cortex and that part of this input may be relayed via CL. We suggest that the excitatory influences of nociceptive and CL stimulation is related to behavioral arousal and attention mechanisms.