Rat Barrel Research Articles

Estimation of thalamocortical and intracortical network models from joint thalamic single-electrode and cortical laminar-electrode recordings in the rat barrel system.

A new method is presented for extraction of population firing-rate models for both thalamocortical and intracortical signal transfer based on stimulus-evoked data from simultaneous thalamic single-electrode and cortical recordings using linear (laminar) multielectrodes in the rat barrel system. Time-dependent population firing rates for granular (layer 4), supragranular (layer 2/3), and infragranular (layer 5) populations in a barrel column and the thalamic population in the homologous barreloid are extracted from the high-frequency portion (multi-unit activity; MUA) of the recorded extracellular signals. These extracted firing rates are in turn used to identify population firing-rate models formulated as integral equations with exponentially decaying coupling kernels, allowing for straightforward transformation to the more common firing-rate formulation in terms of differential equations. Optimal model structures and model parameters are identified by minimizing the deviation between model firing rates and the experimentally extracted population firing rates. For the thalamocortical transfer, the experimental data favor a model with fast feedforward excitation from thalamus to the layer-4 laminar population combined with a slower inhibitory process due to feedforward and/or recurrent connections and mixed linear-parabolic activation functions. The extracted firing rates of the various cortical laminar populations are found to exhibit strong temporal correlations for the present experimental paradigm, and simple feedforward population firing-rate models combined with linear or mixed linear-parabolic activation function are found to provide excellent fits to the data. The identified thalamocortical and intracortical network models are thus found to be qualitatively very different. While the thalamocortical circuit is optimally stimulated by rapid changes in the thalamic firing rate, the intracortical circuits are low-pass and respond most strongly to slowly varying inputs from the cortical layer-4 population.

Hemodynamic Responses of Rat Brain Measured by Near-infrared Spectroscopy During Various Whisker Stimulations

NIRS (Near-infrared spectroscopy) is a relatively, new, non-invasive, and non-ionizing method of measuring hemodynamic responses in thick biological tissues such as the cerebral cortex. In this study, we measured the hemodynamic responses of the rat barrel cortex to whisker stimulation by using a frequency-domain NIRS system. We designed multiple optical probes comprising multi-mode optical fibers and manipulating arms, both of which can be easily applied to small animals. Various electrical stimulations were applied to rat whiskers at different voltage levels and stimulation frequencies. Our results show that the hemodynamic responses are highly dependent on the stimulation voltage level, and not so much on stimulation frequency. This paper suggests that NIRS technology is highly suitable for the study of small animal brains.

Classification of NPY-Expressing Neocortical Interneurons

Neuropeptide Y (NPY) is an abundant neuropeptide of the neocortex involved in numerous physiological and pathological processes. Because of the large electrophysiological, molecular, and morphological diversity of NPY-expressing neurons their precise identity remains unclear. To define distinct populations of NPY neurons we characterized, in acute slices of rat barrel cortex, 200 cortical neurons of layers I-IV by means of whole-cell patch-clamp recordings, biocytin labeling, and single-cell reverse transcriptase-PCR designed to probe for the expression of well established molecular markers for cortical neurons. To classify reliably cortical NPY neurons, we used and compared different unsupervised clustering algorithms based on laminar location and electrophysiological and molecular properties. These classification schemes confirmed that NPY neurons are nearly exclusively GABAergic and consistently disclosed three main types of NPY-expressing interneurons. (1) Neurogliaform-like neurons exhibiting a dense axonal arbor, were the most frequent and superficial, and substantially expressed the neuronal isoform of nitric oxide synthase. (2) Martinotti-like cells characterized by an ascending axon ramifying in layer I coexpressed somatostatin and were the most excitable type. (3) Among fast-spiking and parvalbumin-positive basket cells, NPY expression was correlated with pronounced spike latency. By clarifying the diversity of cortical NPY neurons, this study establishes a basis for future investigations aiming at elucidating their physiological roles.

Early Bilateral Sensory Deprivation Blocks the Development of Coincident Discharge in Rat Barrel Cortex

Several theories have proposed a functional role for synchronous neuronal firing in generating the neural code of a sensory perception. Synchronous neural activity develops during a critical postnatal period of cortical maturation, and severely reducing neural activity in a sensory pathway during this period could interfere with the development of coincident discharge among cortical neurons. Loss of such synchrony could provide a fundamental mechanism for the degradation of acuity shown in behavioral studies. We tested the hypothesis that synchronous discharge of barrel cortex neurons would fail to develop after sensory deprivation produced by bilateral whisker trimming from birth to postnatal day 60. By studying the correlated discharge of cortical neuron pairs, we found evidence for strong correlated firing in control animals, and this synchrony was almost absent among pairs of cortical barrel neurons in deprived animals. The degree of synchrony impairment was different in subregions of rat barrel cortex. The model that best fits the data is that cortical neurons receiving direct inputs from the primary sensory (lemniscal) pathway show the greatest decrement in synchrony following sensory deprivation, while neurons with diverse inputs from other areas of thalamus and cortex are relatively less affected in this dimension of cortical function.

Correlated physiological and perceptual effects of noise in a tactile stimulus

Event Abstract Back to Event Correlated physiological and perceptual effects of noise in a tactile stimulus Comparing neuronal firing parameters with the perceptual report for the same stimuli can be a powerful strategy for uncovering the brain's encoding and decoding mechanisms. The work reported here utilizes that strategy, but with the twist that the neuronal activity is recorded from the whisker-region of rat cortex (barrel cortex) while the perceptual report comes from human subjects. The stimuli in both cases are trains of skin deflections. If the predictions made from the barrel cortex data set are borne out in tests of human tactile perception, we can propose general coding principles that extend across species. We first investigated the responses of neurons in anesthetized rat barrel cortex to trains of whisker deflection, where each train had a periodic temporal structure but was characterized by either a constant-amplitude across all deflections or else variable amplitude (''amplitude noise''). Stimulus trains containing amplitude noise were matched with constant-amplitude trains for mean amplitude but included deflections smaller and larger than the mean. Cortical extracellular responses '' collected from the middle layers '' were equivalent for constant and noisy stimulus trains with frequencies up to 10 Hz. Above 10 Hz, amplitude noise led to a larger response magnitude as well as more prominent firing synchrony. The effects of amplitude noise are thus remarkably similar to those reported earlier for temporal noise: stimulus trains with an irregular sequence of interdeflection intervals evoke a larger and more synchronous cortical response than do frequency-matched periodic stimulus trains (Lak et al., Cerebral Cortex, 2008). The Romo laboratory has shown that in primates the perceived intensity of a train of deflections is correlated with somatosensory cortical firing rate. We predicted therefore that the presence of frequency and amplitude noise would increase response magnitude in human subjects, and that this would lead to an increase in perceived intensity, as compared to matched constant-amplitude or constant-frequency stimuli. We tested this prediction in a series of psychophysical experiments. For each subject, the threshold for detection of amplitude and frequency noise was estimated using a 2-interval forced choice (2AFC) noise detection task. A sub-threshold level of noise was used in the subsequent task. In a standard staircase procedure, subjects were asked to discriminate the intensity of pairs of vibrations delivered to their fingertip in a 2AFC paradigm in which one of the vibrations always had either amplitude or frequency noise while the other vibration did not. The key finding is that, although subjects were unaware of the noise, its presence still caused them to overestimate vibration intensity. Psychophysical effects were comparable '' in the magnitude and direction of perceptual bias '' with those predicted if the physiological effects of stimulus noise seen in barrel cortex were to generalize directly to humans. The main conclusions are that neurons in rat barrel cortex are ''tuned'' to respond in a different way to stimulus trains characterized by temporal and amplitude unpredictability, and that physiological phenomena from barrel cortex can be directly transferred to human tactile system to test hypotheses of perceptual mechanisms. Conference: Computational and systems neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009. Presentation Type: Poster Presentation Topic: Poster Presentations Citation: (2009). Correlated physiological and perceptual effects of noise in a tactile stimulus. Front. Syst. Neurosci. Conference Abstract: Computational and systems neuroscience 2009. doi: 10.3389/conf.neuro.06.2009.03.278 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: 04 Feb 2009; Published Online: 04 Feb 2009. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract Supplemental Data The Authors in Frontiers Google Google Scholar PubMed Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. 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Fast oscillations in the in rat barrel cortex are potentiated by multiple-whisker stimulation

Fast oscillations in the in rat barrel cortex are potentiated by multiple-whisker stimulation

Imaging cortical absorption, scattering, and hemodynamic response during ischemic stroke using spatially modulated near-infrared illumination

We describe a technique that uses spatially modulated near-infrared (NIR) illumination to detect and map changes in both optical properties (absorption and reduced scattering parameters) and tissue composition (oxy- and deoxyhemoglobin, total hemoglobin, and oxygen saturation) during acute ischemic injury in the rat barrel cortex. Cerebral ischemia is induced using an open vascular occlusion technique of the middle cerebral artery (MCA). Diffuse reflected NIR light (680 to 980 nm) from the left parietal somatosensory cortex is detected by a CCD camera before and after MCA occlusion. Monte Carlo simulations are used to analyze the spatial frequency dependence of the reflected light to predict spatiotemporal changes in the distribution of tissue absorption and scattering properties in the brain. Experimental results from seven rats show a 17+/-4.7% increase in tissue concentration of deoxyhemoglobin and a 45+/-3.1, 23+/-5.4, and 21+/-2.2% decrease in oxyhemoglobin, total hemoglobin concentration and cerebral tissue oxygen saturation levels, respectively, 45 min following induction of cerebral ischemia. An ischemic index (I(isch)=ctHHbctO(2)Hb) reveals an average of more then twofold contrast after MCAo. The wavelength-dependence of the reduced scattering (i.e., scatter power) decreased by 35+/-10.3% after MCA occlusion. Compared to conventional CCD-based intrinsic signal optical imaging (ISOI), the use of structured illumination and model-based analysis allows for generation of separate maps of light absorption and scattering properties as well as tissue hemoglobin concentration. This potentially provides a powerful approach for quantitative monitoring and imaging of neurophysiology and metabolism with high spatiotemporal resolution.

Sex difference of the effect of neonatal social isolation on experience driven synaptic delivery of AMPA receptors in rat barrel cortex

Sex difference of the effect of neonatal social isolation on experience driven synaptic delivery of AMPA receptors in rat barrel cortex

Non-homogeneous spatial configuration of vibrissae cortical representation in layer IV of the barrel somatosensory cortex

In the present experiments we studied exclusive and overlapping cortical representational areas of the vibrissae in layer IV cells, across the entire barrel subfield of the rat somatosensory cortex, looking for evidences that would challenge the present assumptions of homogeneity and symmetry among cortical columns in this sensorial system. Our main findings were that in layer IV of the rat barrel cortex: A) Size of vibrissae cortical representational areas (X=0.4174mm(2); SD=0.025) was not homogeneous, vibrissae in dorsal rows (A-B) had significantly smaller areas than those in ventral rows (D-E), a pattern that repeated itself in ares 1-4. B) This difference arises from vibrissal representational overlap, and not from variations in exclusive zones, which are surprisingly homogeneous in size across the barrel cortex (X=0.079mm(2); SD=0.0075); C) The extent of overlapping cortical areas varied systematically, with intra-row overlapping areas having a predominant bias (71.4% of total overlapping) independent of area sizes. Accordingly, vibrissae shared receptive fields with an average of 1.15 vibrissae in the same row and 0.38 in the same are. Barrel cortex has been viewed operationally as a conglomerate of essentially homogenous cortical columns that interact equivalently in the are and row dimensions. Our simple but global cortical reconstructions show that this predominant view should be revised. We postulate that the vibrissae/barrels spatial disposition in rows and ares has a relevant functional meaning, related to different sensory capabilities.

Non-homogeneous spatial configuration of vibrissae cortical representation in layer IV of the barrel somatosensory cortex.

In the present experiments we studied exclusive and overlapping cortical representational areas of the vibrissae in layer IV cells, across the entire barrel subfield of the rat somatosensory cortex, looking for evidences that would challenge the present assumptions of homogeneity and symmetry among cortical columns in this sensorial system. Our main findings were that in layer IV of the rat barrel cortex: A) Size of vibrissae cortical representational areas (X=0.4174mm(2); SD=0.025) was not homogeneous, vibrissae in dorsal rows (A-B) had significantly smaller areas than those in ventral rows (D-E), a pattern that repeated itself in ares 1-4. B) This difference arises from vibrissal representational overlap, and not from variations in exclusive zones, which are surprisingly homogeneous in size across the barrel cortex (X=0.079mm(2); SD=0.0075); C) The extent of overlapping cortical areas varied systematically, with intra-row overlapping areas having a predominant bias (71.4% of total overlapping) independent of area sizes. Accordingly, vibrissae shared receptive fields with an average of 1.15 vibrissae in the same row and 0.38 in the same are. Barrel cortex has been viewed operationally as a conglomerate of essentially homogenous cortical columns that interact equivalently in the are and row dimensions. Our simple but global cortical reconstructions show that this predominant view should be revised. We postulate that the vibrissae/barrels spatial disposition in rows and ares has a relevant functional meaning, related to different sensory capabilities.

Progressive changes in sleep electroencephalogram dynamics in the rat barrel cortex associated with long-term alternation of sensory input activities

Sleep is suggested to be involved in the development and maintenance of neural networks. We investigated how long-term alternation of somatosensory input activities affects electroencephalogram (EEG) dynamics of adult rats during non-REM sleep (NREM). Power spectral densities of NREM EEG activity were analyzed for 10 days under the alternation of sensory input activities caused by unilateral whisker clipping. The progressive reduction of the delta power of the inactivated side of the barrel cortex relative to the activated side was found in terms of the daily mean. This extends our previous study in which only the initial 4-h data in every light period was analyzed. In addition, the circadian variation in power spectral densities of NREM EEG activities in the barrel and visual cortices was found to consist of a common background component and fractional regional difference. Averaging out the background circadian variations and canceling the day-to-day variations and inter-individual differences revealed the progressive monotonic increase and decrease in the delta-band spectral powers in the activated side and inactivated side of barrel cortex, respectively. This concurrent and mutually opposite progressive change in the delta power in NREM might reflect the reorganization process of the cortical circuit, especially inhibitory synaptic transmission, rather than the short-term usage-dependent regional regulation of sleep.

Neuronal Correlates of Local, Lateral, and Translaminar Inhibition with Reference to Cortical Columns

In the neocortex, inhibition by gamma-aminobutyric acidergic (GABAergic) interneurons is essential for shaping cortical maps, which represent sensory signals. For a detailed understanding of the stream of excitation evoked, for example, by a sensory stimulus, interneurons must be identified with reference to their impact on excitatory neurons located in different laminae of the same (home) and surround columns. We analyzed the axonal projection of layer 2/3 (L2/3) interneurons with reference to geometric landmarks of cortical columns by staining neurons in acute slices of rat barrel cortex (P20-P29) and a subsequent cluster analysis using morphological parameters that described the spatial distribution of axons. The cluster analysis defined 4 main axonal projection "types" referred to as 1) "local inhibitors" (including "chandelier neurons"), 2) "lateral inhibitors," 3) "translaminar L2/3-to-L4/5 inhibitors," and 4) "translaminar L2/3-to-L1 inhibitors." The putative innervation domains established by axonal projections of the 4 types of interneurons and the dendritic domains of their target excitatory neurons were 1) L2/3 of the home column, 2) L2/3 of both the home and neighboring columns, 3) L4 and L5A of the home column, and 4) L1 and L2/3 of the home column. The quantitative analysis of the axonal projection patterns of an unselected sample of 51 interneurons located in L2/3 thus defined anatomical correlates for local, lateral, and translaminar inhibition within and between cortical columns.

The Relation between Dendritic Geometry, Electrical Excitability, and Axonal Projections of L2/3 Interneurons in Rat Barrel Cortex

Interneurons in layer 2/3 (L2/3) of the somatosensory cortex show 4 types of axonal projection patterns with reference to the laminae and borders of columns in rat barrel cortex (Helmstaedter et al. 2008a). Here, we analyzed the dendritic geometry and electrical excitability of these interneurons. First, dendritic polarity, measured based on the insertion points of primary dendrites on the soma surface, yielded a continuous one-dimensional measure without a clustering of dendritic polarity types. Secondly, we analyzed polar and vertical distributions of dendritic length. A cluster analysis allowed the definition of 7 types of dendritic arborization. Thirdly, when dendritic polarity was related to the intrinsic electrical excitability we found that the ratio of frequency adaptation in trains of action potentials (APs) evoked by current injection was correlated with the number of primary dendrites. Numerical simulations of spiking patterns in L2/3 interneurons suggested that the number of primary dendrites could account for up to 50% of this correlation. Fourthly, dendritic arborization was not correlated with axonal projection, and axonal projection types could not be predicted by electrical excitability parameters. We conclude that 1) dendritic polarity is correlated to intrinsic electrical excitability, and 2) the axonal projection pattern represents an independent classifier of interneurons.

Efficient Recruitment of Layer 2/3 Interneurons by Layer 4 Input in Single Columns of Rat Somatosensory Cortex

Interneurons in layers 2/3 are excited by pyramidal cells within the same layer (Reyes et al., 1998; Gupta et al., 2000), but little is known about translaminar innervation of these interneurons by spiny neurons in the main cortical input layer 4 (L4). Here, we investigated (1) how efficiently L4 spiny neurons excite L2/3 interneurons via monosynaptic connections, (2) whether glutamate release from axon terminals of L4 spiny neurons depends on the identity of the postsynaptic interneuron, and (3) how L4-to-L2/3 interneuron connections compare with L4-to-L2/3 pyramidal neuron connections. We recorded from pairs of L4 spiny neurons and L2/3 interneurons in acute slices of rat barrel cortex of postnatal day 20 (P20) to P29 rats. The L4-to-L2/3 interneuron connections had an average unitary EPSP of 1.2 +/- 1.1 mV. We found an average of 2.3 +/- 0.8 contacts per connection, and the L4-to-L2/3 interneuron innervation domains were mostly column restricted. Unitary EPSP amplitudes and paired-pulse ratios in the L4-to-L2/3 interneuron connections depended on the "group" of the postsynaptic interneuron. Averaged over all L4-to-L2/3 interneuron connections, unitary EPSP amplitudes were 1.8-fold higher than in the translaminar L4-to-L2/3 pyramidal cell connections. Our results suggest that L4 spiny neurons may more efficiently recruit L2/3 interneurons than L2/3 pyramidal neurons, and that glutamate release from translaminar boutons of L4 spiny neuron axons is target cell specific.

Psychophysical and neurometric detection performance under stimulus uncertainty

Signal detection theoretical analyses of spike counts have revealed that some cortical neurons can exceed psychophysical sensitivity in cases where a sensory signal is specified exactly. It is not known whether this finding holds in the more natural situation where signal occurrence is temporally uncertain. We investigated the ability of rat barrel cortex neurons to detect faint and transient whisker deflections occurring at unspecified times. The progression from fully specified stimuli to temporal uncertainty degraded neuronal sensitivity such that it seems highly unlikely that single neurons can provide the basis for decoding uncertain perceptual events. However, modeling the sensitivity of neuronal pools on basis of spike timing precision across several neurons in an optimal encoding window of 25 ms showed that the subject's perceptual sensitivity could be based on the occurrence of coincident spikes from four to five neurons.

Inter- and Intralaminar Subcircuits of Excitatory and Inhibitory Neurons in Layer 6a of the Rat Barrel Cortex

Approximately half the excitatory neurons in layer 6 (L6) of the rat barrel cortex project to the thalamus with axon collaterals ramifying in the granular L4; the remaining project within cortex with collaterals restricted to infragranular laminae. In analogy, L6 inhibitory neurons also include locally arborizing and inter-laminar projecting neurons. We examined whether L6 neurons participating in different laminar interactions were also morphologically and electrically distinct. Corticothalamic (CT) neurons were labeled by in vivo injections of a retrogradely transported fluorescent tracer into the primary thalamic nucleus. Whole cell current-clamp recordings were performed from labeled and unlabeled L6 neurons in brain slices of juvenile rats; the morphology of cells was subsequently recovered and reconstructed. Corticocortical (CC) neurons were distinguished from CT cells based on the absence of a subcortical projection and the predominantly infragranular arborization of their axon collaterals. Two morphological CC subtypes could be further distinguished based on the structure of their apical dendrite. Electrically, CT neurons had shorter membrane time-constants and action potential (AP) durations and higher rheobase currents. CC neurons fired high-frequency spike doublets or triplets on sustained depolarization; the burst frequency also distinguished the two morphological CC subtypes. Among inhibitory L6 cells, the L4-projecting (L6iL4) and local (L6iL6) inhibitory neurons also had contrasting firing properties; L6iL4 neurons had broader APs and lower maximal firing rates. We propose that L6 excitatory and inhibitory neurons projecting to L4 constitute specialized subcircuits distinct from the infragranular network in their connectivity and firing patterns.

Spatiotemporal distribution of proteoglycans in the developing rat's barrel field and the effects of early deafferentation

The isolectin Vicia villosa B(4) (VV) selectively recognizes N-acetyl-galactosamine-terminal glycoconjugates that form perineuronal nets (PNNs) around a subset of neurons in the cerebral cortex. PNNs are thought to participate in the guidance of incoming thalamic axons and in the posterior stabilization and maintenance of synaptic contacts. Here we examine the spatial and temporal distribution of biotinylated VV in tangential sections through layer IV of the posteromedial barrel subfield in the primary somatosensory cortex (PMBSF) of rats ranging from postnatal day (P)3 to P60, which underwent unilateral deafferentation of whiskers at birth. In the afferented hemisphere, labeling first appears at P5, with a diffuse distribution, probably associated with neuropil, inside PMBSF barrels. VV distribution remains diffuse during the following week, and declines around P17. From P24 onward, however, proteoglycans form PNNs around cell bodies preferentially localized in septal regions of the PMBSF. In the contralateral, deafferented PMBSF the diffuse labeling also appears on P5, but first develops into elongated, homogeneous stripes, which disappear after P24, leaving only scattered cell bodies along layer IV. Our results indicate that proteoglycans appear simultaneous to barrel formation in the developing rat while segregation of PNNs to septal cells might be driven by afferent activity.

Pharmacological modulation of cortical plasticity following kainic acid lesion in rat barrel cortex

The brain shows remarkable capacity for plasticity in response to injury. To maximize the benefits of current neurological treatment and to minimize the impact of injury, the authors examined the ability of commonly administered drugs, dextroamphetamine (D-amphetamine) and phenytoin, to positively or negatively affect the functional recovery of the cerebral cortex following excitotoxic injury. Previous work from the same laboratory has demonstrated reorganization of whisker functional responses (WFRs) in the rat barrel cortex after excitotoxic lesions were created with kainic acid (KA). In the present study, WFRs were mapped using intrinsic optical signal imaging before and 9 days after creation of the KA lesions. During the post-lesion survival period, animals were either treated with intraperitoneal D-amphetamine, phenytoin, or saline or received no treatment. Following the survival period, WFRs were again measured and compared with prelesion data. The findings suggest that KA lesions cause increases in WFR areas when compared with controls. Treatment with D-amphetamine further increased the WFR area (p < 0.05) while phenytoin-treated rats showed decreases in WFR areas. There was also a statistically significant difference (p < 0.05) between the D-amphetamine and phenytoin groups. These results show that 2 commonly used drugs, D-amphetamine and phenytoin, have opposite effects in the functional recovery/plasticity of injured cerebral cortex. The authors' findings emphasize the complex nature of the cortical response to injury and have implications for understanding the biology of the effects of different medications on eventual functional brain recovery.

High-Frequency Whisker Vibration Is Encoded by Phase-Locked Responses of Neurons in the Rat's Barrel Cortex

Rats perform texture discrimination during tactile exploration with their whiskers with high spatial and temporal precision. Although the peripheral mechanoreceptors provide tactile information with exquisite temporal resolution, physiological studies have suggested that this information might be lost at the cortical level. To address this discrepancy, multiunit and single-unit recordings were performed in the barrel cortex of isoflurane-anesthetized rats using continuous sinusoidal vibration of single whiskers at 15-700 Hz. In multiunit recordings, sustained phase-locked responses occurred up to vibration frequencies of 700 Hz, and 1:1 stimulus locking was observed up to 320 Hz. Wide-band responses of multiunits showed frequency encoding between 20 and 320 Hz. The discharge rates were not different for stimuli in the low- and high-frequency ranges, but they were significantly lower for non-phase-locked responses to high-frequency vibration. Response adaptation was present in only 25% of the cases, whereas in the majority of cases, entrainment to the vibratory frequency remained constant or even increased with stimulus duration. Increased entrainment to high-frequency stimulation was accompanied by the emergence of induced activity in the gamma-band range. Analysis of single-unit activity revealed that phase locking to vibratory stimuli was more precise than that observed for the multiunit responses. The results show that whisker vibrations at frequencies above 100 Hz are faithfully encoded by sustained phase-locked responses of cortical neurons under isoflurane anesthesia. It is conceivable that the awake animal makes use of the tactile signals at even much higher frequencies, which can be provided by the peripheral mechanoreceptors during texture discrimination.

Sensation-Targeted Motor Control: Every Spike Counts? Focus on: “Whisker Movements Evoked by Stimulation of Single Motor Neurons in the Facial Nucleus of the Rat”

Traditionally, sensory processing and motor control have been studied separately, reflecting the belief that sensory and motor streams remain independent until linked via cortical “associative” areas. Although this belief no longer dominates neuroscience, the traditional tendency to continue to