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D J Simons

Publications and source records attributed to D J Simons.

34 records · Page 2Linked to original sources
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↗
PubMed1984

Morphology of Golgi-Cox-impregnated barrel neurons in rat SmI cortex.

Golgi-Cox-impregnated neurons in the barrel cortex of the rat were studied qualitatively and quantitatively. Adult rat brains were sectioned perpendicular to or parallel to the cortical representation of the large facial vibrissae at 125 micron. Cortical laminar and barrel boundaries were identified from the Nissl counterstain. Over 200 well-impregnated neurons in cortical layers I-IV were selected for classification and further detailed study. Three broad classes of neurons were recognized: (1) pyramidal cells with conical somata, a stout apical dendrite, and spines; (2) class I nonpyramidal cells having small spherical somata and spiny dendrites; and (3) class II nonpyramidal cells having larger ellipsoid somata and smooth or beaded dendrites. The class I cells were further subdivided into "star pyramids" (cells with an apical dendrite) and spiny stellate cells (cells in which all dendrites were of similar length). The class II cells also were subdivided into multiform cells (with multiple dendrites radiating from the soma) and bipolar cells (with two principal dendritic trunks arising from the superficial and deep aspects of the soma). The position of these various cell types in the superficial cortical laminae was mapped in sections normal to the pia. Numerous examples of the class I and class II neurons were drawn with respect to the barrels in layer IV and the extent of their processes noted. Finally, approximately 250 barrel-related class I and II neurons were studied quantitatively using a computer-microscope and digitizing tablet. The density of the Golgi-impregnated neurons corresponds to the pattern of cell density seen with the Nissl counterstain. The various cell types are not uniformly distributed as a function of cortical depth. Cells with apical dendrites were found principally in the supragranular layers and star pyramids in the superficial one-half of layer IV. Spiny stellate cells are concentrated in layer IV and the smooth cells are present in greatest number in deep layer III and deeper layer IV. On the basis of these distributions we suggest that layer IV be subdivided into two sublaminae. The class I and class II neurons can be distinguished according to quantitative criteria which apply in either plane of section used. Class I neurons have smaller projected somal areas, more proximal dendritic branching, and shorter dendrites when class I and II neurons are measured in three dimensions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Functional organization of mouse and rat SmI barrel cortex following vibrissal damage on different postnatal days.

This study was undertaken to determine the functional properties of neurons in the anatomically altered somatosensory cortex after neonatal whisker damage. In mice and rats neonatal lesions of the facial vibrissae change the anatomical organization of barrels in the contralateral SmI cortex. These changes depend on the pattern and severity of the peripheral damage and the developmental age of the animals. To understand some of the functional correlates of these anatomical changes, the middle row of vibrissae (row C) was damaged in mice on postnatal days 1, 3, and 5 and in rats on postnatal days 1 and 5. The receptive field properties of single cortical units were studied after the animals matured. In 24 mice and 15 rats a total of 1,370 units were characterized in microelectrode penetrations which passed through the somatosensory cortex either tangential or perpendicular to the pia. Units were localized anatomically with respect to both barrel and laminar boundaries, and the extent of the peripheral damage was assessed histologically. The data revealed an orderly representation of the sensory periphery that coincided with the altered cytoarchitectonic organization of the SmI cortex. Specifically: (1) Units in the enlarged row B or row D barrels responded primarily to row B or row D whiskers. (2) In layer IV, units in the altered row C cortex either could not be reliably driven from the periphery, were activated by stimulation of scar tissue in the damaged facial row C, or were driven by adjacent, intact row B or row D whiskers. (3) Units in supra- and infragranular layers either had no row C representation or incorporated scar tissue in their receptive fields in a topographically correct fashion. Responses of units to stimulation of scar tissue were qualitatively similar to those elicited from intact vibrissae, which also activated them. (4) In SmII, units that responded to whiskers had receptive fields whose organization matched the representation of the periphery observed in SmI. (5) There was no mapping of nonmystacial pad structures in the barrel cortex, and there were no units with abnormal multiwhisker interactions when laminar boundaries were taken into account. These data indicate that neonatal damage to the whiskers alters both the anatomical arrangement of the barrels and the physiologically determined somatotopic representation of the sensory periphery in a parallel and predictable fashion.

Age Factors↗
PubMed1983

Multi-whisker stimulation and its effects on vibrissa units in rat SmI barrel cortex.

Ceramic piezoelectric 'bimorphs' were used to construct multiangular mechanical stimulators which are small enough to attach to separate, adjacent vibrissae on the mystacial face pad of rodents. Use of two stimulators to independently deflect pairs of whiskers revealed that the responses of SmI cortical vibrissa units are determined by the direction in which both hairs are moved, the spatial sequence of the displacements, and the particular combination of whiskers that are stimulated. The stimulators can thus serve as the basic elements in a large array of independently controllable whisker deflectors.

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↗
PubMedDate not supplied

Early experience of tactile stimulation influences organization of somatic sensory cortex.

Visual experience is essential for the establishment of the cerebral cortical circuitry that allows normal binocular vision. For example, the pattern of right-eye, left-eye dominance columns is permanently altered by simply closing an eye of a young primate. A critical issue is whether environmental factors also influence the development of other cortical sensory areas. In the present experiments we manipulated the tactile experience of young rats by depriving them of the sensory information that is normally provided by their large facial whiskers. Electrophysiological analyses showed that simply trimming the whiskers from the day of birth results in pronounced abnormalities in the response properties of single neurons in the adult somatic sensory cortex. Thus functional plasticity in response to early experience appears to be a fundamental aspect of cortical development.

Animals↗