Response Properties Of Units Research Articles

Chronic intraventricular administration of lysergic acid diethylamide (LSD) affects the sensitivity of cortical cells to monocular deprivation

In kittens, but not in adult cats, depriving one eye of pattern vision by suturing the lids shut (monocular deprivation or MD) for one week reduces the proportions of binocular units in the visual cortex. A sensitivity of cortical units in adult cats to MD can be produced by infusing exogenous monoamines into the visual cortex 23. Since LSD interacts with monoamines, we have examined the effects of chronic administration of LSD on the sensitivity to MD for cortical cells in adult cats. Cats were assigned randomly to one of four conditions: MD/LSD, MD/No-LSD, No-MD/No-LSD. An osmotic minipump delivered either LSD or the vehicle solution alone during a one-week period of MD. The animals showed no obvious anomalies during the administration of the drug. After one week the response properties of single units in urea 17 of the visual cortex were studied without knowledge of the contents of the individual minipumps. With the exception of ocular dominance, the response properties of units recorded in all animals did not differ from normal. In the control animals (MD/No-LSD, No-MD/LSD, No-MD/No-LSD) the average proportion of binocular cells was 78%; similar to that observed for normal adult cats. However, in the experimental animals, which received LSD during the period of MD, only 52% of the cells were binocular. Our results suggest that chronic intraventricular administration of LSD affects either directly or indirectly the sensitivity of cortical neurons to MD.

Intracerebral influences on the microstructure of receptive fields of cat visual cortex.

Effects of electrical stimulation of the basal ganglia (caudate nucleus and putamen) and cortex (gyrus proreus and compositus) on the receptive fields and response properties of units in the visual cortex of cats were assessed using single lines, double lines and multiple lines (gratings). In the single line experiment caudate stimulation, significantly increased the spontaneous activity, optimal firing rate and receptive field size of visual cortex neurons whereas putamen stimulation decreased these parameters. Stimulation of gyrus proreus enhanced, while that of gyrus compositus diminished optimal firing rate without affecting spontaneous activity; in addition, stimulation of ipsilateral proreus and compositus increased the receptive field size whereas their contralateral homologues decreased it. In the double line experiment, proreus and caudate stimulation increased the magnitude of the facilitatory effect of progressive separation of the lines over certain ranges whereas compositus and putamen stimulation increased the inhibitory influences. Orientation selectivity and spatial frequency tuning characteristics were unaffected by the electrical stimulation of any of the four sites. Thus three categories of network properties were delineated: those characterized by remaining invariant to any cerebral stimulation; those characterized by overall activation as by basal ganglia stimulation; and those characterized as interactive which were responsive especially to cortical stimulation.

Single unit responses to linear frequency-modulations in the inferior colliculus of the Greater horseshoe bat,Rhinolophus ferumequinum

1. Recordings were made from 135 single inferior colliculus neurons of the Greater horseshoe bat,Rhinolophus ferrumequinum. These bats emit sonar signals which are characterized by a long constant frequency (CF-) component and a terminal frequency modulated (FM-) component. The responses of the units to CF- and FM-stimuli with different modulation heights, durations and directions were studied. 2. The majority of single units studied had minimum thresholds that were either equal for CF- and FM-signals of the same duration or lower for the CF-stimulus. Only rarely was the sensitivity for FM-signals higher than for a CF-signal. 3. With FM-signals the response properties of units with best frequencies between 65–81 kHz, i.e. in the frequency range of the FM-component of the echolocation call, did not differ significantly from units with best frequencies in lower frequency ranges. Relatively many units with best frequencies in the filter region of the audiogram (81–88 kHz) required FM-signals with particular modulation heights and rates to elicit excitatory responses. 4. Response patterns and spike count functions were found to differ with CF- vs. FM-signals. The most common difference was a smaller number of impulses per stimulus and a temporally more restricted (‘phasic’) discharge pattern to FM-signals than to CF-signals. Greater discharge activity to FM-signals occurred in only a few units. ‘Latency constant’ and ‘FM-specialized’ neurons, as reported for other species were also found. 5. Inhibition was frequently observed with FM-stimuli in spontaneously active neurons. An accurate prediction of a neuron's response to FM-signals from knowledge of the excitatory and inhibitory response areas to CF-signals was not always possible. 6. The responses of ‘FM-specialized’ neurons to the FM-component of a CF-FM-stimulus was not significantly altered by the presence of a CF-component in the filter region of the audiogram. 7. Responses of single units to signal and noise combinations are described. 8. Data are discussed in relation to results on the processing of FM-signals in other bats.

Electrical stimulation of the eighth nerve in cat: Temporal properties of unit responses in the large spherical cell region of the AVCN

Single‐unit responses to intracochlear electrical stimulation were studied. Responses were highly phase‐locked to sinusoidal stimulation at frequencies less than 4 kHz. At any given stimulus frequency, synchronization indexes were greater than those that have been reported for eighth nerve responses to acoustic stimuli. At the onset of a low‐frequency (i.e., below 800 Hz) sinusoidal stimulus, firing rate gradually increased over many tens of milliseconds. Rise times were as long as 50–100 ms for low‐intensity, low‐frequency sinusoidal stimulus bursts. At greater intensities and/or higher stimulus frequencies, the response rise times were considerably shorter. Preliminary results indicate that responses to trains of short‐duration biphasic pulses do not exhibit such slow rise times. These results may relate to Eddington's [Ann. Otol. Rhinol. Laryngol. 87 (Suppl. 53), 1–37 (1978)] finding that behavioral threshold increases sharply as the burst duration of a sinusoidal stimulus is decreased. However, threshold is only a weak function of the duration of a train of short‐duration biphasic pulses. For sinusoids below 300 Hz, multiple discharges per cycle were common at levels considerably above threshold. [Work supported by NIH.]

Responses of single neurons in physiologically defined primary auditory cortex (AI) of the cat: frequency tuning and responses to intensity.

Responses of single neurons in physiologically defined primary auditory cortex (AI) of the cat: frequency tuning and responses to intensity.

Anatomical distribution and sensory properties of brain stem and posterior diencephalic neurons responding to genital, somatosensory, and nociceptive stimulation in the squirrel monkey

In chloralose-urethane-anesthetized female squirrel monkeys, 325 single units sampled from a region extending from the caudal medulla to the posterior diencephalon were examined for responsiveness to genital, rectal, innocuous somatosensory, and various forms of nociceptive stimulation. The units were highly responsive, with 84% responding to at least one stimulus type. The responsive units were widely distributed in the brain stem tegmentum, deep tectum, and posterior diencephalon. Very few neurons responded to only one type of stimulation. The patterns of convergent responsiveness to the various stimulus types were not, however, a simple random function of unit responsiveness to each type of stimulus per se. Unit responses to vaginal stimulation consisted of simple increases or decreases in firing which outlasted the duration of the probing stimulus in most cases. Some units responded more strongly to cervical than to vaginal tract stimuli. The somatic receptive fields of units responding to touch-pressure stimuli were typically bilateral and quite extensive. A forceps pinch of nociceptive intensity elicited a response from 64% of the cells, and of these, 11% showed significant linear correlations between their firing rates and increasing pinch pressure in the nociceptive intensity range. Brief, localized nociceptive thermal stimuli and needle pricks failed to elicit responses from the neurons tested. Based on a comparison between the response properties of monkey brain stem neurons and the previous findings for rat and cat neurons, it was concluded that brain stem cells display species-typical sensory characteristics which have parallels in the properties of behavioral responses of these three species to genital and other sensory stimuli. Properties of unit responses to nociceptive stimuli have implications in relation to the neural mechanisms of first and second pain.

Response properties of units in the lateral geniculate nucleus of the domestic chick ( Gallus domesticus)

One hundred and four visual units of the (ventral) lateral geniculate nucleus (GL) of chicks (Gallus domesticus) were studied with extracellular microelectrodes. Most were extremely responsive to moving targets even at low speeds (0.1 degrees/sec). They were classified as follows. (1) movement-sensitive units with uniform, restricted receptive fields (47%). (2) Movement-sensitive units with small receptive fields possessing regions responding to differing modes of stimulation ('center-periphery units'). (3) Movement-sensitive neurons with uniform, wide receptive fields, larger than 75 degrees x 65 degrees (15%). (4) Movement-insensitive cells, responsive only to illumination changes (7%). (5) Units with indeterminate receptive fields, a poor visual response or a poor response to movement (14%). The firing of neurons in classes I-III was mostly an accurate function of target speed; half of them also provided accurate monitoring of the beginning, course and termination of target movement (tonic units). In view of the above, the high proportion of directionally selective cells (31%) and the large size of many of its receptive fields, the GL is considered as a candidate structure for optomotor integration but the evidence is otherwise scant. There is, however, an apparent contribution to its unit properties from both retinal ganglion cells and neurons from different tectal layers. Whatever its role, it is unlikely to be the functional homologue to the mammalian ventral lateral geniculate as the unit properties of two structures differ substantially.

Representation of the cochlea within the anterior auditory field (AAF) of the cat

The anterior auditory field (AAF) is a large auditory representation in the cerebral cortex of the cat rostral to the ‘primary’ auditory cortex (AI) on the middle and anterior ectosylvian gyri. Fine-grained microelectrode maps of unit best frequencies were made in AAF of 16 ketamine anesthetized cats. Among the results were the following. (1) Most units in AAF that were driven by tonal stimuli had tuning curves with a single, sharply definable minimum (the best frequency). Occasionally, units were found to have multiple tuning curve minima. (2) In penetrations normal to the cortical surface of AAF, isolated units had remarkably similar tuning curves througout the middle and deep cortical layers. (3) In most of AAF, a restricted sector of the cochlear partition is represented by a straight belt of cortex crossing the entire field. (4) There is a highly ordered representation of the cochlea within AAF. The cortical belt representing the most basal sector of the cochlea (highest best frequencies) is oriented dorsoventrally along the border with the high frequency region of AI. Proceeding rostrally for some distance with AAF, lower frequency cortical belts are parallel to one another and maintain a highly ordered representation of progressively more apical cochlear sectors. The orientation of the lowest frequency representation usually rotates following the ventral curvature of the anterior ectosylvian gyrus. (5) In the portion of the field caudal to the axis of rotation of the representation, best frequency (represented cochlear position) is a simple (and apparently relatively constant) function of distance from the mutual high frequency AI-AAF border. (6) There is a propootionately larger representation of the highest frequency octaves within AAF. (7) The results of penetrations down the banks of the suprasylvian sulcus indicate that there may be units of vertical organization within AAF similar to those in AI, and in somatosensory and visual cortical fields. (8) The boundaries of AAF as well as the frequency representation within it are highly variable when referenced to cortical surface landmarks. (9) The cytoarchitectonic boundaries of AAF approximately correspond with the physiologically defined boundaries. (10) There were no cells driven to discharge by tonal stimuli in the fields dorsal and ventral to AAF. Comparison of the properties of AAF and AI show that these two fields are remarkably similar in many important features including unit response properties under ketamine anesthesia, short latency to earliest unit discharge, organization in depth, units of vertical organization, size, spatial representation of frequency and proportionately greater representation of higher frequency octaves. They also share some common thalamocortical inputs. These similarities suggest that AAF is not a ‘secondary’ cortical field, but, rather, that AAF and AI are virtually mirror images of one another and are co-participants in the earliest and fundamental processing of acoustic information at the cortical level.

Dynamic properties of the responses of single neurones in the cochlear nucleus of the rat.

1. The dynamic properties of unit responses to amplitude-modulated tones were studied using modulation with pseudorandom noise and described by cross-covariance and integrated cross-covariance functions between the discharge rate and the modulation. Under the experimental conditions used, these two functions are valid approximations of the system's impulse and step response functions respectively. 2. On the basis of their impulse response functions units could be classified into two groups, Type I with a low adaptation and Type II with a large degree of adaptation as well as a damped oscillation in their impulse response functions. 3. The response pattern of the Type II units is most likely the result of a negative feed-back striving to keep the discharge rate at a nearly constant level. 4. The cross-covariance functions are shown to remain unchanged during long duration recordings from the same unit.

Statistical evaluation of the dynamic properties of cochlear nucleus units using stimuli modulated with pseudorandom noise

A method is described for studying the dynamic properties of unit responses using sounds which are amplitude modulated with pseudorandom noise. It is based on computation of cross-correlation functions between the signal modulating the stimulus and the neural discharge frequency. The discharge frequency is represented by a cycle histogram of the neural discharges locked to the repetition of the noise. Transfer functions of the system under test are obtained on the basis of the spectrum of the computed cross-correlation functions. The results obtained using this method in study of the dynamic properties of the responses of single units in the cochlear nucleus of the rat were compared with results obtained using sounds modulated with sinusoids. The dynamic properties were described by gain functions showing the ratio between the degree of modulation of the neural discharge frequency and the degree of amplitude modulation of the tone. The results using these two methods were similar. It was furthermore found that the reproducibility of the results over several hours was good. It is concluded that the responses of these units can be described using linear system theory when the modulation depth is kept low. In many units the dynamic properties become a function of the sound intensity. A transfer function may thus only be a valid description of the dynamic properties of a unit at a certain stimulus level. The advantages of using random noise signals in studies of the dynamic properties compared with sinusoidal modulation signals are discussed.

Unimodal and multimodal response properties of neurons in the cat's superior colliculus

Cells in the upper layers of the superior colliculus of the cat were found to be exclusively responsive to visual stimuli, whereas neurons responsive to visual or nonvisual stimuli (or both) were encountered in the deeper laminae. Bimodal and trimodal units were located and their response and receptive field properties were described. The response probabilities and receptive field characteristics of neurons located in the deeper laminae differed from those usually encountered in the upper laminae of the superior colliculus and in primary sensory projection nuclei. Visual receptive fields of multimodal units were often large and, in many instances, did not even approach the high response probability to successive identical stimuli, which was characteristic of neurons in the upper laminae. The somatic receptive fields of both unimodal and multimodal units were large, sometimes discontinuous, and appeared to have properties strikingly different from those described in the lemniscal system. The effects of cooling the visual cortex upon unimodal and multimodal unit response properties were investigated and were found to selectively depress responsiveness to visual stimuli while responsiveness to auditory and somatic stimuli remained unaltered.

Response properties of units in the dorsal column nuclei of the freely moving rat: changes as a function of behaviour

Response properties of units in the dorsal column nuclei of the freely moving rat: changes as a function of behaviour