Multiple Single-unit Recordings Research Articles

Sequential reinstatement of neocortical activity during slow oscillations depends on cells’ global activity

During Slow Wave Sleep (SWS), cortical activity is dominated by endogenous processes modulated by slow oscillations (0.1–1 Hz): cell ensembles fluctuate between states of sustained activity (UP states) and silent epochs (DOWN states). We investigate here the temporal structure of ensemble activity during UP states by means of multiple single unit recordings in the prefrontal cortex of naturally sleeping rats. As previously shown, the firing rate of each PFC cell peaks at a distinct time lag after the DOWN/UP transition in a consistent order. We show here that, conversely, the latency of the first spike after the UP state onset depends primarily on the session-averaged firing rates of cells (which can be considered as an indirect measure of their intrinsic excitability). This latency can be explained by a simple homogeneous process (Poisson model) of cell firing, with sleep averaged firing rates employed as parameters. Thus, at DOWN/UP transitions, neurons are affected both by a slow process, possibly originating in the cortical network, modulating the time course of firing for each cell, and by a fast, relatively stereotyped reinstatement of activity, related mostly to global activity levels.

Thalamocortical interactions in first- and higher order thalamic nuclei

Event Abstract Back to Event Thalamocortical interactions in first- and higher order thalamic nuclei Péter Barthó1*, István Ulbert2 and László Acsády1 1 Hungarian Academy of Sciences, Institute of Experimental Medicine, Hungary 2 Hungarian Academy of Sciences, Institute of Psychology, Hungary During natural sleep and anesthesia, neocortical activity is characterized by periods of synchronized activity alternating with periods of silence (up- and down-states). Despite being the most numerous input source and output target of the cortex, the relation of thalamus to synchronized cortical activity is not yet fully established. Thalamic nuclei differ in their connectivity; first order (FO) thalamic nuclei receive driving inputs from various subcortical centers whereas higher order (HO) nuclei are contacted by driving afferents arising from cortical layer V. Besides, all thalamic nuclei receive strong modulatory input from cortical layer VI. To investigate thalamocortical synchrony, we performed simultaneous multiple single-unit recordings in rats under urethane anesthesia in the somatosensory FO ventral postero-medial nucleus (VPM), the HO nucleus posterior (Po) and in the S1 cortex. The recordings were made using four-shank silicon probes, which could span different nuclei. The exact electrode position was determined by pre-labeling the probes with DiI. In Po, thalamic relay activity showed up-and down states, with majority of cells firing phase locked to cortical activity. In VPM, however, thalamic firing was weakly coupled to cortical up- and down states. Instead, the activity was dominated by local spindles, which were frequently restricted to one or two electrode shanks, and only occasionally spread to the neocortex. In the VPM another type of unit was also recorded with narrower spike waveforms, longer burst duration, and higher activity during spindles. These features indicate that they can potentially be the axon terminals of reticular thalamic neuron Relay cells and putative nRt terminals fired at different phases of spindle oscillations, with relay cells preceding nRt terminals. Our data demonstrate distinct population activity in first order, higher order and reticular thalamic nuclei. Conference: IBRO International Workshop 2010, Pécs, Hungary, 21 Jan - 23 Jan, 2010. Presentation Type: Poster Presentation Topic: Sensory and motor systems Citation: Barthó P, Ulbert I and Acsády L (2010). Thalamocortical interactions in first- and higher order thalamic nuclei. Front. Neurosci. Conference Abstract: IBRO International Workshop 2010. doi: 10.3389/conf.fnins.2010.10.00062 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 21 Apr 2010; Published Online: 21 Apr 2010. * Correspondence: Péter Barthó, Hungarian Academy of Sciences, Institute of Experimental Medicine, Budapest, Hungary, bartho@koki.hu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Péter Barthó István Ulbert László Acsády Google Péter Barthó István Ulbert László Acsády Google Scholar Péter Barthó István Ulbert László Acsády PubMed Péter Barthó István Ulbert László Acsády Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

A selective allosteric potentiator of the M1 muscarinic acetylcholine receptor increases activity of medial prefrontal cortical neurons and restores impairments in reversal learning.

M(1) muscarinic acetylcholine receptors (mAChRs) may represent a viable target for treatment of disorders involving impaired cognitive function. However, a major limitation to testing this hypothesis has been a lack of highly selective ligands for individual mAChR subtypes. We now report the rigorous molecular characterization of a novel compound, benzylquinolone carboxylic acid (BQCA), which acts as a potent, highly selective positive allosteric modulator (PAM) of the rat M(1) receptor. This compound does not directly activate the receptor, but acts at an allosteric site to increase functional responses to orthosteric agonists. Radioligand binding studies revealed that BQCA increases M(1) receptor affinity for acetylcholine. We found that activation of the M(1) receptor by BQCA induces a robust inward current and increases spontaneous EPSCs in medial prefrontal cortex (mPFC) pyramidal cells, effects which are absent in acute slices from M(1) receptor knock-out mice. Furthermore, to determine the effect of BQCA on intact and functioning brain circuits, multiple single-unit recordings were obtained from the mPFC of rats that showed BQCA increases firing of mPFC pyramidal cells in vivo. BQCA also restored discrimination reversal learning in a transgenic mouse model of Alzheimer's disease and was found to regulate non-amyloidogenic APP processing in vitro, suggesting that M(1) receptor PAMs have the potential to provide both symptomatic and disease modifying effects in Alzheimer's disease patients. Together, these studies provide compelling evidence that M(1) receptor activation induces a dramatic excitation of PFC neurons and suggest that selectively activating the M(1) mAChR subtype may ameliorate impairments in cognitive function.

Characterizing multiple-unit activity in the anterior cingulate cortex during choice behavior as a stochastic nonlinear process

Successful decision-making requires an ability to monitor contexts, actions and outcomes, functions in which the anterior cingulate cortex (ACC) plays a critical role. There is accumulating evidence that the transient organization of neurons into dynamic ensembles and the sequential transitions among them may form the basis for cortical information processing [1-3]. Recently, we analyzed the population activity obtained from multiple single-unit recordings from the rat ACC during performance of an ecologically valid decision making task [2]. We showed that ensembles of neurons move through different coherent and dissociable states as the cognitive requirements of the task change. This organization into distinct network patterns with respect to firing rate changes broke down on trials with numerous behavioral errors, especially at choice points of the task. So far, in this and other studies, state spaces were examined that were direct representations of the multiple-unit activity (MUA) with dimensions directly corresponding to the instantaneous firing rates of all simultaneously recorded units. These spaces were then visualized using dimensionality reduction techniques like metric multi dimensional scaling and analyzed using multivariate statistics like linear discriminant functions [2,3]. However, there is also evidence that, for instance temporary synchrony among neurons down to the millisecond level and locked to specific behavioral events [4], plays an important role in neural information processing. These highly non-stationary properties of the MUA time series are not or only implicitly contained in previous state space approaches, a problem which some groups started to address [5]. Therefore, the temporal dynamics of ACC neurons and their functioning as an integrated network are still poorly understood. A more indepth understanding might be achieved by new algorithms that fuse statistical learning with nonlinear time series analysis methods. Here, we propose a new modelfree multivariate nonlinear stochastic time series algorithm for the analysis of those simultaneous multiple single-unit recordings. It produces a low-dimensional state space that is optimal with regards to several dynamical properties of the multiple recorded units. Our results show that not only successful choice behavior, as it was demonstrated in [2], but also the incorrect choice behavior in challenging situations can be visually and effectively characterized as attracting sets in a suitable coordinate map, but with important differences to the state space characterization of MU activity during correct choice behavior. These methods also suggest ways to accurately predict behavior based on the state space trajectories obtained from the neural ensemble dynamics.

Organization of Color-Selective Neurons in Macaque Visual Area V4

Cortical area V4 in monkeys contains neurons that respond selectively to particular colors. It has been controversial how these color-selective neurons are spatially organized in V4. One view asserts that color-selective neurons are organized in columns with different colors orderly mapped across the cortex, whereas other studies have found no evidence for columnar organization or any other clustered structure. In the present study, we reexamined the functional organization of color-selective neurons in area V4 by quantitatively evaluating and comparing the color selectivity of nearby neurons as well as those encountered along electrode penetrations. Using a multiple single-unit recording technique, we recorded extracellular activities simultaneously from groups of nearby V4 neurons. Color discrimination and color preferences exhibited a moderate correlation between nearby neurons, consistent with neurons in a local region of V4 sharing similar responses to stimulus color. However, the degree of clustering was variable across recording sites. Some regions contained neurons with similar color preferences, whereas others contained neurons with diverse color preferences. Neurons in penetrations normal to the cortical surface responded to an overlapping range of colors and maintained a moderate correlation. Neurons in penetrations tangential to the cortical surface differed dramatically in their preferred color and exhibited a negative correlation. We conclude that neurons in area V4 are moderately clustered according to their color selectivity and that this weak clustering is columnar in structure.

IMPROVED FLEXIBLE MICROWIRE ARRAY ELECTRODE FOR INTRACORTICAL SIGNALS RECORDING

Implanted electrodes are the first piece of hardware in an intracortical signals recording pathway. This work presents an improved flexible microwire array electrode for intracortical recordings. Only ready-made materials and general mechanical tools are used to fabricate a microelectrode. The proposed procedure is relatively simple, even for a novice worker to implement in-house. Many key steps in producing a good microwire array electrode are facilitated. These main steps include selecting materials, preparing for fabrication, and assembling the electrode. The assembly of the microwire array electrode includes connecting and positioning PCB pattern, arraying and fixing microwires, and soldering and packaging the electrode. A practiced researcher can assemble the microelectrode in about 2 h and implant it in approximately three. The mass of this assembled microelectrode is 1.96 g. The cost of the materials in the entire array is less than US$1.5, and the array is suitable for implantation in the cortex of rats for invasive studies. In this study, electrochemical impedance spectroscopy is also applied to measure the impedance and the phase between the electrode and the electrolyte, and then to obtain an equivalent circuit. The improved microwire array electrode is adopted to record the intracortical signal of cerebrum. The microwire array electrode can be fabricated and used for multi-site, multiple single-unit recording experiments. Several experimental results are presented, along with applications that demonstrate the feasibility and advantages of the proposed approach.

Morphine Modulation of Pain Processing in Medial and Lateral Pain Pathways

BackgroundDespite the wide-spread use of morphine and related opioid agonists in clinic and their powerful analgesic effects, our understanding of the neural mechanisms underlying opioid analgesia at supraspinal levels is quite limited. The present study was designed to investigate the modulative effect of morphine on nociceptive processing in the medial and lateral pain pathways using a multiple single-unit recording technique. Pain evoked neuronal activities were simultaneously recorded from the primary somatosensory cortex (SI), ventral posterolateral thalamus (VPL), anterior cingulate cortex (ACC), and medial dorsal thalamus (MD) with eight-wire microelectrode arrays in awake rats.ResultsThe results showed that the noxious heat evoked responses of single neurons in all of the four areas were depressed after systemic injection of 5 mg/kg morphine. The depressive effects of morphine included (i) decreasing the neuronal response magnitude; (ii) reducing the fraction of responding neurons, and (iii) shortening the response duration. In addition, the capability of cortical and thalamic neural ensembles to discriminate noxious from innocuous stimuli was decreased by morphine within both pain pathways. Meanwhile, morphine suppressed the pain-evoked changes in the information flow from medial to lateral pathway and from cortex to thalamus. These effects were completely blocked by pre-treatment with the opiate receptor antagonist naloxone.ConclusionThese results suggest that morphine exerts analgesic effects through suppressing both sensory and affective dimensions of pain.

Task and context encoding by medial prefrontal cortex ensembles

Event Abstract Back to Event Task and context encoding by medial prefrontal cortex ensembles Jeremy Seamans1* 1 University of British Columbia, Canada Like humans, the behavior of many animals is guided by rules. The first rules we learn are often very simple and involve learning that a particular response leads to reward. Prior to language development these early rules are acquired through trial and error learning. The flexible implementation of rules is thought to rely on the prefrontal cortex (PFC). We obtained multiple single-unit recordings of PFC neurons as rats acquired a novel rule through trial and error learning. While single units could be quite rule selective, the ensemble of units was always far more so. During the trial and error learning period, the ensemble gradually moved away from representing the first rule to the point where an abrupt transition occurred and the ensemble shifted to a new state where it began to encode the new rule. This “a-ha” moment captured by our analyses was in some animals preceded by a third stable network state, in between the two rule representations that was highly variable, perhaps indicative of a neural search. The transitions in the neural trajectories were closely associated with the animal’s behavior. These data therefore provide insights into how simple types of trial and error rule learning are accomplished within the brain. Conference: Conference on Neurocognitive Development, Berkeley, CA, United States, 12 Jul - 14 Jul, 2009. Presentation Type: Oral Presentation Topic: Cognitive control frontostriatal circuitry, and dopamine Citation: Seamans J (2009). Task and context encoding by medial prefrontal cortex ensembles. Conference Abstract: Conference on Neurocognitive Development. doi: 10.3389/conf.neuro.09.2009.10.014 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 06 Jul 2009; Published Online: 06 Jul 2009. * Correspondence: Jeremy Seamans, University of British Columbia, Vancouver, Canada, jeremyseamans@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Jeremy Seamans Google Jeremy Seamans Google Scholar Jeremy Seamans PubMed Jeremy Seamans Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The Role of Sound in Adult and Developmental Auditory Cortical Plasticity

The purpose of the current review is to highlight the role of the acoustic environment in auditory cortical plasticity. In order do this we have reviewed our past studies on auditory cortical plasticity based on long-latency evoked potential recordings in humans following cochlear implantation, and multiple single-unit recordings from cat auditory cortex following noise trauma and exposure to a non-deafening acoustic environment. The results of these studies, and those of other investigators highlighted here, show that the auditory cortex shows plastic changes throughout life. Those that occur during maturation are typically considered the most profound and long lasting. In that case plasticity is beneficial as it allows adaptation to behaviorally important sound and adapts easily to changes induced by deafness and subsequent application of hearing aids or cochlear implants. In children as well as adults, changes in cortical representation of frequency can occur following hearing loss, but may be accompanied by unpleasant side effects such as tinnitus. Long exposure to a spectrally enhanced acoustic environment of moderate sound level that does not cause hearing loss paradoxically also results in pronounced changes in the cortical tonotopic maps. These changes are very similar to those following noise trauma. This review provides evidence that in adults, long-lasting plastic changes in auditory cortex occur even in the absence of behaviorally relevant acoustic stimulation. However, in children, the long lasting absence of auditory stimulation arrests cortical development.

COMPARISON OF PRIMARY AND SECONDARY SOMATOSENSORY CORTICAL RESPONSES TO FOREPAW STIMULATION

Two cortical regions, primary somatosensory (S1) and secondary somatosensory cortex (S2), are engaged in coding somatosensory information in all mammals. Although the role of S1 has been extensively reported, the anatomical and functional knowledge for S2 remained to be determined. Our aim was to investigate how S2 participates in information processing by comparing with corresponding S1 region. Ensemble neuronal activities of S1 and S2 forepaw regions were obtained by multiple-channel multiple single-unit recording method, and electrical stimulations of various intensities were applied to the forepaw. Several similarities between stimulation-evoked S2 and S1 neuronal responses were found. First, S2 neurons' activations were with similar onset and peak latencies in comparison with those of the S1 neurons at all intensities tested. Second, S2 and S1 neurons showed statistically indistinguishable half maximum duration. In addition, neurons in both areas responded to electrical stimulation with similar response magnitude. Finally, the response magnitude of S2 and S1 neurons showed comparable variation with increasing stimulation intensity. This similarity in response patterns between S1 and S2 neurons to peripheral stimulation suggested that S2 and S1 shared comparable hierarchy in anatomical and functional aspects in the somatosensory system.

Successful choice behavior is associated with distinct and coherent network states in anterior cingulate cortex

Successful decision making requires an ability to monitor contexts, actions, and outcomes. The anterior cingulate cortex (ACC) is thought to be critical for these functions, monitoring and guiding decisions especially in challenging situations involving conflict and errors. A number of different single-unit correlates have been observed in the ACC that reflect the diverse cognitive components involved. Yet how ACC neurons function as an integrated network is poorly understood. Here we show, using advanced population analysis of multiple single-unit recordings from the rat ACC during performance of an ecologically valid decision-making task, that ensembles of neurons move through different coherent and dissociable states as the cognitive requirements of the task change. This organization into distinct network patterns with respect to both firing-rate changes and correlations among units broke down during trials with numerous behavioral errors, especially at choice points of the task. These results point to an underlying functional organization into cell assemblies in the ACC that may monitor choices, outcomes, and task contexts, thus tracking the animal's progression through "task space."

Responses of infragranular neurons in the rat primary somatosensory cortex to forepaw and hindpaw tactile stimuli

Infragranular layers constitute the main output of the primary somatosensory cortex and represent an important stage of cortico-cortical and cortico-subcortical integration. We have previously used chronic multiple single-unit recordings to study the spatiotemporal structure of tactile responses of infragranular neurons within the forepaw cortical representation in rats [Tutunculer B, Foffani G, Himes BT, Moxon KA (2006) Structure of the excitatory receptive fields of infragranular forelimb neurons in the rat primary somatosensory cortex responding to touch. Cereb Cortex 16:791–810]. Here we extend our understanding of this structure by studying the overlap between the forepaw and hindpaw cortical representations. We recorded 204 responsive neurons in chronic experiments from eight anesthetized rats. Overall, only 23% of neurons responded exclusively to one paw, 52% of neurons responded to two paws, 19% of neurons responded to three paws, and 5% of neurons responded to all four paws. Quantitative measures of response magnitudes and latencies revealed the following main results. (1) The responses of forepaw neurons overall displayed greater magnitudes and shorter latencies than the responses of hindpaw neurons. (2) The responses to ipsilateral stimuli displayed smaller magnitudes, and longer—and more variable—latencies than the responses to contralateral stimuli. (3) The responses of forepaw neurons to hindpaw stimuli displayed smaller magnitudes and longer latencies than the responses to forepaw stimuli, whereas the responses of hindpaw neurons to forepaw stimuli displayed smaller magnitudes but similar latencies compared with the responses to hindpaw stimuli. These results show that the spatiotemporal structure of tactile responses of infragranular neurons extends across all four paws, and provide the basic architecture for studying physiological integration and pathophysiological reorganization of tactile information in the infragranular layers of the rat primary somatosensory cortex.

Large-Scale Chronically Implantable Precision Motorized Microdrive Array for Freely Behaving Animals

Multiple single-unit recording has become one of the most powerful in vivo electro-physiological techniques for studying neural circuits. The demand has been increasing for small and lightweight chronic recording devices that allow fine adjustments to be made over large numbers of electrodes across multiple brain regions. To achieve this, we developed precision motorized microdrive arrays that use a novel motor multiplexing headstage to dramatically reduce wiring while preserving precision of the microdrive control. Versions of the microdrive array were chronically implanted on both rats (21 microdrives) and mice (7 microdrives), and relatively long-term recordings were taken.

Detecting synfire chain activity using massively parallel spike train recording.

The synfire chain model has been proposed as the substrate that underlies computational processes in the brain and has received extensive theoretical study. In this model cortical tissue is composed of a superposition of feedforward subnetworks (chains) each capable of transmitting packets of synchronized spikes with high reliability. Computations are then carried out by interactions of these chains. Experimental evidence for synfire chains has so far been limited to inference from detection of a few repeating spatiotemporal neuronal firing patterns in multiple single-unit recordings. Demonstration that such patterns actually come from synfire activity would require finding a meta organization among many detected patterns, as yet an untried approach. In contrast we present here a new method that directly visualizes the repetitive occurrence of synfire activity even in very large data sets of multiple single-unit recordings. We achieve reliability and sensitivity by appropriately averaging over neuron space (identities) and time. We test the method with data from a large-scale balanced recurrent network simulation containing 50 randomly activated synfire chains. The sensitivity is high enough to detect synfire chain activity in simultaneous single-unit recordings of 100 to 200 neurons from such data, enabling application to experimental data in the near future.

Comparing the prefrontal cortex of rats and primates: Insights from electrophysiology

There is a long-standing debate about whether rats have what could be considered a prefrontal cortex (PFC) and, if they do, what its primate homologue is. Anatomical evidence supports the view that the rat medial PFC is related to both the primate anterior cingulate cortex (ACC) and the dorsolateral PFC. Functionally the primate and human ACC are believed to be involved in the monitoring of actions and outcomes to guide decisions especially in challenging situations where cognitive conflict and errors arise. In contrast, the dorsolateral PFC is responsible for the maintenance and manipulation of goal-related items in memory in the service of planning, problem solving, and predicting forthcoming events. Recent multiple single-unit recording studies in rats have reported strong correlates of motor planning, movement and reward anticipation analogous to what has been observed in the primate ACC. There is also emerging evidence that rats may partly encode information over delays using body posture or variations in running path as embodied strategies, and that these are the aspects tracked by medial PFC neurons. The primate PFC may have elaborated on these rudimentary functions by carrying them over to more abstract levels of mental representation, more independent from somatic or other external mnemonic cues, and allowing manipulation of mental contents outside specific task contexts. Therefore, from an electrophysiological and computational perspective, the rat medial PFC seems to combine elements of the primate ACC and dorsolateral PFC at a rudimentary level. In primates, these functions may have formed the building blocks required for abstract rule encoding during the expansion of the cortex dorsolaterally.

Cerebellar Dysfunction Explains the Extinction-Like Abolition of Conditioned Eyeblinks After NBQX Injections in the Inferior Olive

Classical conditioning of the eyeblink response is a form of motor learning that is controlled by the intermediate cerebellum and related brainstem structures. The inferior olive (IO) is commonly thought to provide the cerebellum with a "teaching" unconditioned stimulus (US) signal required for cerebellar learning. Testing this concept has been difficult because the IO, in addition to its putative learning function, also controls tonic activity in the cerebellum. Previously, it was reported that inactivation of AMPA/kainate receptors in the IO produces extinction of conditioned responses (CRs), suggesting that it blocks the transmission of US signals without perturbing the functional state of the cerebellum. However, the electrophysiological support for this critical finding was lacking, mostly because of methodological difficulties in maintaining stable recordings from the same set of single units throughout long drug injection sessions in awake rabbits. To address this critical issue, we used our microwire-based multiple single-unit recording method. The IO in trained rabbits was injected with the AMPA/kainate receptor blocker, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX), and its effects on CR expression and neuronal activity in the cerebellar interposed nuclei (IN) were examined. We found that NBQX abolished CR expression and that delayed drug effects were independent of the presentation of the conditioned stimulus and were therefore not related to extinction. In parallel to these behavioral effects, the spontaneous neuronal activity and CR-related neuronal responses in the IN were suppressed, suggesting cerebellar dysfunction. These findings indicate that testing the role of IO in learning requires methods that do not alter the functional state of the cerebellum.

COMPARISON OF PRIMARY AND SECONDARY SOMATOSENSORY CORTICAL RESPONSES TO FOREPAW STIMULATION

Two cortical regions, primary somatosensory (S1) and secondary somatosensory cortex (S2), are engaged in coding somatosensory information in all mammals. Although the role of S1 has been extensively reported, the anatomical and functional knowledge for S2 remained to be determined. Our aim was to investigate how S2 participates in information processing by comparing with corresponding S1 region. Ensemble neuronal activities of S1 and S2 forepaw regions were obtained by multiple-channel multiple single-unit recording method, and electrical stimulations of various intensities were applied to the forepaw. Several similarities between stimulation-evoked S2 and S1 neuronal responses were found. First, S2 neurons' activations were with similar onset and peak latencies in comparison with those of the S1 neurons at all intensities tested. Second, S2 and S1 neurons showed statistically indistinguishable half maximum duration. In addition, neurons in both areas responded to electrical stimulation with similar response magnitude. Finally, the response magnitude of S2 and S1 neurons showed comparable variation with increasing stimulation intensity. This similarity in response patterns between S1 and S2 neurons to peripheral stimulation suggested that S2 and S1 shared comparable hierarchy in anatomical and functional aspects in the somatosensory system.

Quantitative analysis of functional clustering of neurons in the macaque inferior temporal cortex

Neurons with similar preferences for two-dimensional shapes of intermediate complexity cluster in area TE of the monkey inferior temporal cortex. To further characterize the functional structure of area TE, we quantitatively analyzed various aspects of the visual responses of closely located neurons by applying multiple single-unit recording techniques in anesthetized monkeys. Examination of the visual responses elicited with a large, predetermined set of visual stimuli confirmed previous findings that nearby neurons, on average, exhibited positively correlated preferences for a set of visual stimuli. Nearby neurons also tended to be similar in their receptive-field organization and contrast-polarity preference. In contrast, no correlation was found in the size tuning of neighboring neurons. Pooling or subtraction of activities between a pair of nearby neurons was shown to improve stimulus discriminability, if the neuron pair had positively or negatively correlated stimulus preferences, respectively. These results indicate that nearby TE neurons share some aspects of stimulus preference, but their response selectivity differ in other aspects. Both pooling and subtraction between nearby neurons can reduce across-trial response variability, if these decoding strategies are applied to appropriate neuronal pools.

Barosensitive neurons in the rat tractus solitarius and paratrigeminal nucleus: a new model for medullary, cardiovascular reflex regulation.

The nucleus of the solitary tract (NTS), a termination site for primary afferent fibers from baroreceptors and other peripheral cardiovascular receptors, contains blood pressure-sensitive neurons, some of which have rhythmic activity locked to the cardiac cycle, making them key components of the central pathway for cardiovascular regulation. The paratrigeminal nucleus (Pa5), a small collection of medullary neurons in the dorsal lateral spinal trigeminal tract, like the NTS, receives primary somatosensory inputs of glossopharyngeal, vagal, and other nerves. Recent studies show that the Pa5 has efferent connections to the rostroventrolateral reticular nucleus (RVL), NTS, and ambiguous nucleus, suggesting that its structure may play a role in the baroreceptor reflex modulation. In the present study, simultaneous recording from multiple single neurons in freely behaving rats challenged with i.v. phenylephrine administration, showed that 83% of NTS units and 72% of Pa5 units were baroreceptor sensitive. Whereas most of the baroreceptor-sensitive NTS and Pa5 neurons (86 and 61%, respectively) increased firing rate during the ascending phase of the pressor response, about 16% of Pa5 and NTS baroreceptor-sensitive neurons had a decreased firing rate. On one hand, the decrease in firing rate occurred during the ascending phase of the pressor response, indicating sensitivity to rapid changes in arterial pressure. On the other hand, the increases in neuron activity in the Pa5 or NTS occurred during the entire pressor response to phenylephrine. Cross-correlational analysis showed that 71% of Pa5 and 93% of NTS baroreceptor-activated neurons possessed phasic discharge patterns locked to the cardiac cycle. These findings suggest that the Pa5, like the NTS, acts as a terminal for primary afferents in the medullary-baroreflex or cardiorespiratory-reflex pathways.

A simple method for fabricating horizontal and vertical microwire arrays

Microwire array electrodes are important in multi-site, multiple single-unit recording experiments. A simple method is described herein for the construction of microwire arrays consisting of evenly spaced insulated microwires in either horizontal or vertical orientations. Several key steps in the fabrication of a good microwire array electrode are made easier with this method. These steps include (1) arranging microwires into a desirable configuration, (2) keeping track of microwire sequences, and (3) soldering microwires to closely packed slots. This method needs only general mechanical tools and is relatively simple even for inexperienced workers.