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D J Simons

Publications and source records attributed to D J Simons.

At least 19 recordsLinked to original sources
PubMed1992

Responses of barrel cortex neurons in awake rats and effects of urethane anesthesia.

A "barrel" is an interconnected network of layer IV neurons that is an important component of a functional cortical column in the whisker area of the rodent primary somatosensory cortex. The present study was undertaken in order to resolve apparently conflicting findings from single-unit studies of barrel neurons conducted in rats maintained under different anesthetic conditions. Multiunit responses to controlled deflections of mystacial vibrissae were recorded from the whisker/barrel cortex of awake, undrugged rats, and responses at the same recording site were reexamined after the animal was anesthetized with urethane. In contrast to the awake condition, stimulus-evoked responses under urethane were characterized by a large late component. Such effects were more pronounced for deflections of noncolumnar or "adjacent" whiskers than for the columnar whisker. Latencies to peak responses were virtually identical for the columnar whisker in awake and urethane states (11.9 vs 11.8 ms) but were considerably longer for adjacent whisker deflections in urethane-anesthetized animals (15.5 vs 29.0 ms). The magnitudes of adjacent whisker responses, relative to the response evoked by the columnar whisker, varied with the laminar location of the recording site in awake but not in urethane-anesthetized animals; in awake rats, receptive fields were clearly smallest in the layer IV barrels. Results in the awake condition confirm those of previous studies conducted in unanesthetized or lightly sedated animals, and data obtained with urethane are comparable to others' results in urethane-anesthetized rats. The former have important implications for how barrel cortex processes information in behaving animals.

Anesthesia↗
PubMed1991

Functional asymmetries in the rodent barrel cortex.

Neurophysiological and 2-deoxyglucose (2DG) studies of the rodent whisker barrel cortex have demonstrated asymmetries in its functional organization. To examine the possibility that the activity gradients observed in metabolic studies can be attributed to subtle rostral-caudal and dorsal-ventral asymmetries in electrophysiologically measured surround or cross-whisker inhibition, we compared 2DG results with predictions generated from quantitative single-cell receptive field data. Despite differences in the two experimental approaches, there is remarkable agreement between the findings. (1) The distribution of 2DG activity declines across the barrel cortex of the behaving animal from anteromedial barrels to posterolateral barrels, and is qualitatively and quantitatively similar to the values predicted from neurophysiology. (2) The strength of surround inhibition in barrel neurons predicts the twofold increase in activation of the C3 barrel following acute clipping of adjacent whiskers. And (3) within a cortical column, the decrease in metabolic activity associated with adjacent whisker stimulation is greatest in layer IV and least in the infragranular layers; this corresponds to the laminar distribution of inhibitory interactions observed electrophysiologically.

Afferent Pathways↗
PubMed1991

Electromyographic activity of mystacial pad musculature during whisking behavior in the rat.

Cinematographic measurements of whisker movements generated by behaving rats were compared with electromyographic (EMG) activity recorded simultaneously from mystacial pad musculature. Muscle activity consisted of repetitive bursts, each of which initiated a "whisking" cycle consisting of a protraction followed by a retraction. Protraction amplitude and velocity were directly proportional to the amount of EMG activity during forward whisker movement. Overtime, the intensity of muscle discharge determined the set point about which the vibrissae moved; higher levels of muscle activity resulted in a greater degree of overall whisker protraction. These findings are consistent with the known anatomy of the facial musculature and underscore the importance of whisker protraction in the acquisition of tactile information by the vibrissae.

Animals↗
PubMed1990

Responses of rat trigeminal ganglion neurons to movements of vibrissae in different directions.

The response properties of 123 trigeminal ganglion neurons were studied, using controlled whisker deflections in different directions. When the distal end of the whisker was initially displaced 5.7 degrees (1 mm) from its neutral position, 81% of the cells responded with statistically more spikes/stimulus to movements in one to three of eight cardinal (45 degrees increment) directions than to the others. The more directionally selective the cell, the more vigorous was its response. On the basis of statistical criteria, 75% of the cells were classified as slowly adapting, 25% as rapidly adapting. A number of quantitative analyses indicated that slowly adapting units respond more selectively than rapidly adapting cells to the direction of whisker movement. Differences in directional sensitivities of rapidly and slowly adapting cells appear to parallel differences between their putative mechanoreceptive endings and the relationships between those endings and the vibrissa follicle's structure. Comparisons between the response properties of peripheral and central neurons in the vibrissa-lemniscal system indicate that the afferent neural signal is progressively and substantially transformed by mechanisms that function to integrate information from different peripheral receptors and from different, individual vibrissae.

Action Potentials↗
PubMed1990

Biometric analyses of vibrissal tactile discrimination in the rat.

Blindfolded rats were trained to stretch across a gap to palpate rough or smooth surfaces with their mystacial vibrissae. Animals learned to discriminate reliably a smooth surface from a rough surface having shallow (approximately 30 microns) grooves spaced at 90 microns intervals. Field-by-field video analyses confirmed that rats used only their vibrissae to contact the discriminanda. The whiskers swept across the surfaces at 696 degrees/sec during forward movements and 1106 degrees/sec for retracting movements. Mean amplitudes, which were 32 degrees, were considerably smaller than the total arc through which whiskers can move. Rats maintained whisker contact with discriminanda for several hundreds of msec, during which time the animals repetitively swept their vibrissae across the surface at a dominant frequency of 8 Hz. The range extended from 1 to 20 Hz, and the frequencies utilized varied within and among subjects. Whiskers contacted the discriminanda along the hair shaft, not at the whisker tips. The hair shafts were bent continually but to varying degrees as an animal palpated the surface, and more than one of the large caudal whiskers were almost always in contact with it. Thus, whiskers are not used independently as rigid levers. Results indicate that the capacity of the rodent whisker system to distinguish a smooth surface from a rough one is comparable to that of primates using their fingertips and suggest common strategies for active touch in the mammalian somatomotor system.

Animals↗
PubMed1989

Spatial organization of thalamocortical and corticothalamic projection systems in the rat SmI barrel cortex.

Axonal tracing techniques were used to examine the distribution of corticothalamic projection neurons in relation to the organization of the thalamocortical recipient zones in the whisker representation of the rat first somatic sensory cortex. Following injection of horseradish peroxidase into the physiologically defined vibrissa area in the ventrobasal complex of the thalamus, labeling in the cortex had a columnar appearance. Dense patches of anterograde labeling were located within the centers of the layer IV barrels and extended superficially through lamina III; the septa between barrels contained considerably less reaction product. Retrogradely labeled neurons were observed in lower layer V and layer VI where they were concentrated preferentially deep to the barrel centers. Regions deep to the septa displayed less overall labeling and a lower relative number of thalamic projecting neurons. Zones having the larger numbers of retrogradely labeled cells also contained terminallike labeling of either corticothalamic or thalamocortical origin. Following an injection that included the posterior group medial to the ventrobasal complex, anterograde labeling in layer IV was located largely in the septa. In conjunction with previous findings concerning the origin and termination of other projection systems in the barrel cortex, these results suggest that a vibrissal column contains a central core zone intimately linked with the ventrobasal thalamus that is bounded by narrower regions of more diverse inputs and outputs that form an interface between adjacent cortical columns.

Animals↗
PubMed1989

Thalamocortical response transformation in the rat vibrissa/barrel system.

1. Extracellular single-unit recordings and controlled whisker stimuli were used to compare response properties between cells in the "barreloids" of the thalamic ventrobasal complex and those in the cytochrome oxidase-rich centers of the "barrels" in the first somatic sensory cortex. Individual vibrissae were deflected alone or in paired combination involving the neuron's maximally excitatory whisker and an adjacent one in the same or neighboring whisker rows. Quantitative data were derived from 135 thalamocortical unit's (TCUs), 242 "regular-spike" barrel units (RSUs), and 16 "fast-spike" barrel units (FSUs) recorded in 26 normal adult rats. 2. Compared with TCUs, RSUs displayed lower rates of spontaneous activity and responded less vigorously to whisker stimuli. Proportionally, more than twice as many TCUs as RSUs responded in slowly adapting fashion to at least one angular direction of whisker displacement. Discharges of slowly adapting TCUs were approximately 3.5 times greater than those of slowly adapting RSUs. 3. Proportionally, about twice as many TCUs than RSUs responded selectively to whisker movements in different angular directions. 4. Cells in the thalamus responded more vigorously to a larger number of whiskers than RSUs in the cortex. Depending on the stimulus conditions, two to three times more TCUs than RSUs were excited by two or more whiskers. 5. Following displacement of an adjacent whisker, unit discharges to subsequent deflections of the maximally excitatory whisker were reduced in a time-dependent fashion. The time course of response suppression was similar in TCUs and RSUs, but inhibitory interactions between adjacent whiskers were observed much less often in the thalamus. A cyclic pattern of stimulus-evoked excitation/inhibition characterizes responses in the cortical barrels but is considerably less pronounced in the thalamic barreloids. 6. The presence and/or degree of response suppression depended on which adjacent whisker was stimulated and on the angular direction of that whisker's movement. For individual TCUs, some adjacent whiskers evoked inhibition, others did not. The vast majority of RSUs displayed response suppression to all adjacent whiskers. Unlike receptive fields of TCUs, those of RSUs have small--i.e., single-whisker--excitatory centers with potent and symmetrical inhibitory surrounds. 7. Fast-spike units in the barrels displayed the greatest spontaneous and stimulus-evoked activities and were the least selective for whisker movements at different angular directions. FSUs had the largest excitatory receptive fields; 100% responded to two or more vibrissae.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Membrane potential changes in rat SmI cortical neurons evoked by controlled stimulation of mystacial vibrissae.

Intracellular recordings from rat somatic sensory vibrissa/barrel cortex demonstrate that whisker displacements evoke short latency excitatory postsynaptic potentials followed by longer lasting inhibitory potentials. The time course and whisker-related spatial distribution of the potentials represent synaptic correlates of the integration of whisker inputs observed in extracellular studies.

Animals↗
PubMed1987

Thalamic and corticocortical connections of the second somatic sensory area of the mouse.

Thalamic and corticocortical connections of the second somatic sensory area (SII) in the mouse cerebral cortex were investigated by means of the retrograde transport of horseradish peroxidase. Focal injections of the enzyme were made in physiologically determined locations within the parietal cortex. Results show that SII receives substantial inputs from topographically appropriate regions within the ipsilateral ventrobasal nucleus and from the ipsilateral posterior group. The limb representation, which was previously found to be responsive to auditory stimulation, received inputs also from the medial division of the medial geniculate body. The SII face representation, which is largely unresponsive to auditory stimuli, received little or no input from the medial geniculate body. SII injections yielded retrograde labeling in the topographically appropriate region in the first somatic sensory area (SI), and SI injections retrogradely labeled cells in SII in a pattern consistent with previous electrophysiological maps. Homotypical regions within SI and SII therefore appear to be reciprocally interconnected. SII also receives inputs from the ipsilateral motor cortex and from contralateral SI and SII. Finally, injections into the SI paw but not face regions yielded retrograde labeling in the thalamic ventrolateral nucleus. Thus, the distal limb representations in SI and SII each receive inputs from a third major relay nucleus (i.e., medial geniculate to SII, ventrolateral nucleus to SI) whereas the face representations do not. These results indicate a close functional interrelationship between homotypical areas in SI and SII, though the two areas differ in several important respects. It is proposed that SII in mice may complement the function of SI by helping to define the overall sensory context in which detailed tactile discriminations are made.

Animals↗
PubMed1987

A reliable technique for marking the location of extracellular recording sites using glass micropipettes.

A simple and highly reliable technique is described for marking the locations of extracellularly recorded neurons using double-barreled glass micropipettes. One barrel contains 3 M NaCl for recording; the other contains horseradish peroxidase (HRP) that is iontophoretically ejected using low currents. With appropriate processing of the tissue, small well-localized spots are produced that contain a small number of HRP-filled neurons. The technique is effective in marking sequential recording sites within individual electrode tracks and in multiple penetrations using the same microelectrode.

Action Potentials↗
PubMed1986

Somatotopic organization of the second somatosensory area (SII) in the cerebral cortex of the mouse.

The somatotopic organization of the parietal cortex of barbiturate-anesthetized, adult mice was studied using tungsten microelectrodes. A complete representation of the contralateral face and body occupying approximately 4.0-4.5 mm2 was found immediately posterior and lateral to the representation of the face in the first somatosensory area (SI). Within this second somatosensory area (SII), the following findings were made: A relatively large region is devoted to representations of the paws and face, especially the sinus hairs associated with the anterior upper lip and mystacial vibrissae. Receptive fields on these body regions are among the smallest found in SII, though larger than corresponding receptive fields in SI. In particular, vibrissae receptive fields always include at least several adjacent whiskers, and paw receptive fields always include at least two adjacent digits. In regions representing proximal body parts, receptive fields are considerably larger, may include both contralateral and ipsilateral limb or trunk surfaces, and sometimes include the entire body and face. Responses to both somatosensory and auditory stimulation were consistently found in the body (i.e., trunk and limb) representation, but rarely found in the face region. The face is represented most anteriorly, and the hindlimb and tail most posteriorly. Forepaw and hindpaw digits and anterior aspects of the face (e.g., perioral sinus hairs and the incisors) are represented laterally, while the back, caudal head, and mystacial vibrissae are represented medially. Within SII, therefore, a "musculus" can be viewed as having an upright body orientation with the face area bordering the face representation within SI. By comparison with SI, SII is characterized by a less pronounced layer IV, which is of irregular thickness and packing density, and by less uniformity in the layering of pyramidal cells in lamina V. In addition, SII is generally thicker from pia to white matter than SI. These results are in general accord with earlier findings from evoked potential studies in mice, but are at variance with recent reports in mice and rats that the mystacial vibrissae have only a minimal, or no, representation within SII. Indeed, the present findings suggest that the representation of the whiskers in SII may have a specialized function paralleling that in SI.

Afferent Pathways↗
PubMed1985

Metabolic and structural correlates of the vibrissae representation in the thalamus of the adult rat.

Cytochrome oxidase (CO) histochemistry was used to examine patterns of metabolic activity in the ventral posteromedial nucleus of the adult rat thalamus. In sections cut in an oblique horizontal plane, CO staining reveals distinct patches of heightened activity arranged in a fashion remniscent of the pattern of vibrissae on the contralateral face and which corresponds to the known somatotopic organization of the nucleus. The CO-reactive zones coincide with oval cylinders of thalamic neurons that appear to be anatomically linked with corresponding barrels in the contralateral somatosensory cortex.

Afferent Pathways↗
PubMed1985

Metabolic activity in SmI cortical barrels of adult rats is dependent on patterned sensory stimulation of the mystacial vibrissae.

Cytochrome oxidase (CO) histochemistry was used to examine the effect of sensory deprivation on metabolic activity in the somatosensory cortex (SmI) of adult rats. Chronic trimming of one or several rows of mystacial vibrissae resulted in a decrease in CO reactivity in the corresponding barrels in layer IV. Reduced CO staining also was observed in cortical laminae superficial and deep to the affected layer IV barrels, suggesting that patterned deflections of the whiskers are important for maintaining the metabolic activity of neurons at least 3 and perhaps 4 synapses removed from the periphery.

Animals↗
PubMed1985

Cytochrome oxidase staining in the rat SmI barrel cortex.

Patterns of cytochrome oxidase (CO) activity were examined histochemically in the rat SmI cortex. Discrete regions of high enzymatic activity were centered upon the granule cell aggregates (barrels) in layer IV. Those barrels which correspond to the mystacial vibrissae and make up the posteromedial barrel subfield (PMBSF) were especially interesting in that CO staining revealed distinct metabolic subdivisions which do not have an easily demonstrable cytoarchitectonic counterpart. By analogy with the barrels in mouse PMBSF and with the cytoarchitectonically distinct barrels representing the smaller sinus hairs in the rat we propose that regions of high CO activity denote the "hollow" of the rat PMBSF barrels. In accord with previous physiological studies demonstrating a vertical organization in the rodent barrel cortex, we also noted columns of intense CO activity extending from layer VI through sublamina Vb. The centers of these columns coincided with the centers of the barrels in layer IV. In tangential sections through the infragranular laminae the segmentation of CO-positive zones was less distinct than in layer IV and appeared as bands of heightened activity oriented like the five rows of layer IV barrels. Highly reactive somata and dendrites were observed in both the granular and infragranular CO barrels indicating that some of the increased activity of these regions reflects oxidative metabolism of cortical neurons per se. These patterns of metabolic activity underscore the vertical and horizontal organization of the SmI vibrissa cortex and suggest that neurons located within the central core of a column have functional properties distinct from those located in zones where individual columns interface.

Animals↗
PubMed1985

Temporal and spatial integration in the rat SI vibrissa cortex.

Glass micropipettes were used to record the activity of 124 single units in the somatosensory vibrissa cortex (SI) of 16 rats in response to combined deflections of contralateral vibrissae. Compact multiangular electromechanical stimulators were used to stimulate individual vibrissal hairs alone or in combinations of two or three adjacent whiskers. Each whisker was stimulated independently to produce controlled temporal and spatial patterns of mechanical stimuli. Following displacement of a vibrissa, unit discharges to subsequent deflections of adjacent whiskers are reduced in a time-dependent fashion. Response suppression is strongest at short interdeflection intervals, i.e., 10-20 ms and decreases progressively during the 50-100 ms following the first deflection. In many cases this period also corresponds with a reduction in ongoing unit discharges. Response suppression was not observed for first-order neurons recorded in the trigeminal ganglion of barbiturate-anesthetized rats. In the cortex, the presence and/or degree of response suppression depends on a number of spatial factors. These include 1) the angular direction(s) in which the individual hairs are moved, 2) the sequence in which two whiskers are deflected, that is, which one is deflected first, 3) the particular combination of whiskers stimulated, and 4) the number (2 or 3) of vibrissae comprising the multiwhisker stimulus. Within a vertical electrode penetration, one particular whisker typically elicits the strongest excitatory and inhibitory effects; other, nearby vibrissae elicit variable (or no) excitation or inhibition. Excitatory and inhibitory subregions of a receptive field could thus be distributed asymmetrically around the maximally effective whisker. In these cases, the receptive fields displayed spatial orientations. Quantitative criteria were used to classify 30 cortical units on the basis of the distribution of inhibitory subregions on either side of the maximally effective whisker. Twenty-one of these cells had receptive fields (RFs) with symmetrical inhibitory side regions. Responses of the other nine units were strongly suppressed by a preceding deflection of a vibrissa on one side but relatively unaffected, or even slightly facilitated, by preceding deflection of the whisker on the other side.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1978

Response properties of vibrissa units in rat SI somatosensory neocortex.

1. Glass microelectrodes were used to record extracellular responses from 308 SI cortical neurons to deflections of the contralateral vibrissae in 21 unanesthetized, paralyzed rats. Controlled deflections of individual hairs were produced by means of an electromechanical stimulator. Fast green dye marks were made to aid histological reconstructions of electrode tracks. 2. TS) were observed throughout layers II--VI; "fast" cortical spikes (FS) were less frequently encountered and largely restricted to layer IV. Although both types of potentials had similar negative-positive waveforms. FSs were distinguished from RSs by their comparatively rapid time course, about half that of RSs. RS units (RSU) discharged spontaneously at rates of less than 1--15/s, whereas FS units (FSU) displayed rates of 15--50/s. The amplitudes of FSs, which were generally smaller than those of RSs, often decreased during high-frequency discharges. 3. With sinusoidal oscillations of a vibrissa FSUs responded more reliably and over a broader range of frequencies (3 to at least 40 Hz) than did RSUs , particularly in layer IV. In addition, FSUs typically responded to whisker deflections over a range of 360 degrees, whereas many RSUs in layer IV displayed sharp spatial-tuning charcteristics, responding over a restricted range of less than 90 degrees. 4. Of all units, 58% responded preferentially to stimulus transients (vibrissal movements), 32% displayed sustained responses to stimulus stead-states (fixed vibrissal displacement). For the remaining 10% of units the appropriate stimulus could not be specified; these units were particularly common in layer V. 5. Computation of quantitative stimulus-response relations showed that many units increased their rate of discharge with increasing stimulus intensities. 6. Most units were directionally selective, responding preferentially to deflections of a whisker in one or more of four quadrants. 7. In radial penetrations through the cortex there was a columnar patern so that units were activated at least by the same (i.e., the "principal") whisker. In a number of cases these could be directly correlated with the barrels. Of all units, 55% responded to deflections of single vibrissa only, the remaining 45% to 2--12 adjacently situated vibrissae. For most multiple-whiser units the responses elicited by deflection of any one hair activating the neuron was qualitatively similar to those elicited by deflection of any other hair activating it. The principal whisker of the penetration was typically associated with the most vigorous responses. 8. In layer IV, 85% of neurons responded to deflections of one hair only, the remaining 15% to two or more hairs. In layers II and III 39% of units were activated by more than one vibrissa; in layers V and VI multiple-whisker units predominated (64%). Whisker configurations in the deep layers were larger than those in other layers. 9...

Animals↗