Biomedical subjects

O Favorov

Publications and source records attributed to O Favorov.

10 recordsLinked to original sources

PubMed1999

SI neuron response variability is stimulus tuned and NMDA receptor dependent.

Skin brushing stimuli were used to evoke spike discharge activity in single skin mechanoreceptive afferents (sMRAs) and anterior parietal cortical (SI) neurons of anesthetized monkeys (Macaca fascicularis). In the initial experiments 10-50 presentations of each of 8 different stimulus velocities were delivered to the linear skin path from which maximal spike discharge activity could be evoked. Mean rate of spike firing evoked by each velocity (MFR) was computed for the time period during which spike discharge activity exceeded background, and an across-presentations estimate of mean firing rate (MFR) was generated for each velocity. The magnitude of the trial-by-trial variation in the response (estimated as CV; where CV = standard deviation in MFR/MFR) was determined for each unit at each velocity. MFR for both sMRAs and SI neurons (MFRsMRA and MFRSI, respectively) increased monotonically with velocity over the range 1-100 cm/s. At all velocities the average estimate of intertrial response variation for SI neurons (CVSI) was substantially larger than the corresponding average for sMRAs (CVsMRA). Whereas CVsMRA increased monotonically over the range 1-100 cm/s, CVSI decreased progressively with velocity over the range 1-10 cm/s, and then increased with velocity over the range 10-100 cm/s. The position of the skin brushing stimulus in the receptive field (RF) was varied in the second series of experiments. It was found that the magnitude of CVSI varied systematically with stimulus position in the RF: that is, CVSI was lowest for a particular velocity and direction of stimulus motion when the skin brushing stimulus traversed the RF center, and CVSI increased progressively as the distance between the stimulus path and the RF center increased. In the third series of experiments, either phencylidine (PCP; 100-500 microg/kg) or ketamine (KET; 0.5-7.5 mg/kg) was administered intravenously (iv) to assess the effect of block of N-methyl-D-aspartate (NMDA) receptors on SI neuron intertrial response variation. The effects of PCP on both CVSI and MFRSI were transient, typically with full recovery occurring in 1-2 h after drug injection. The effects of KET on CVSI and MFRSI were similar to those of PCP, but were shorter in duration (15-30 min). PCP and KET administration consistently was accompanied by a reduction of CVSI. The magnitude of the reduction of CVSI by PCP or KET was associated with the magnitude of CVSI before drug administration: that is, the larger the predrug CVSI, the larger the reduction in CVSI caused by PCP or KET. PCP and KET exerted variable effects on SI neuron mean firing rate that could differ greatly from one neuron to the next. The results are interpreted to indicate that SI neuron intertrial response variation is 1) stimulus tuned (intertrial response variation is lowest when the skin stimulus moves at 10 cm/s and traverses the neuron's RF center) and 2) NMDA receptor dependent (intertrial response variation is least when NMDA receptor activity contributes minimally to the response, and increases as the contribution of NMDA receptors to the response increases).

Action Potentials↗

PubMed1994

The tactile movement aftereffect.

The existence of a tactile movement aftereffect was established in a series of experiments on the palmar surface of the hand and fingers of psychophysical observers. During adaptation, observers cupped their hand around a moving drum for up to 3 min; following this period of stimulation, they typically reported an aftereffect consisting of movement sensations located on and deep to the skin, and lasting for up to 1 min. Preliminary experiments comparing a number of stimulus materials mounted on the drum demonstrated that a surface approximating a low-spatial-frequency square wave, with a smooth microtexture, was especially effective at inducing the aftereffect; this adapting stimulus was therefore used throughout the two main experiments. In Experiment 1, the vividness of the aftereffect produced by 2 min of adaptation was determined under three test conditions: with the hand (1) remaining on the now stationary drum; (2) in contact with a soft, textured surface; or (3) suspended in air. Subjects' free magnitude estimates of the peak vividness of the aftereffect were not significantly different across conditions; each subject experienced the aftereffect at least once under each condition. Thus the tactile movement aftereffect does not seem to depend critically on the ponditions of stimulation that obtain while it is being experienced. In Experiment 2, the vividness and duration of the aftereffect were measured as a function of the duration of the adapting stimulus. Both measures increased steadily over the range of durations explored (30-180 sec). In its dependence on adapting duration, the aftereffect resembles the waterfall illusion in vision. An explanation for the tactile movement aftereffect is proposed, based on the model of cortical dynamics of Whitsel et al. (1989, 1991). With assumed modest variation of one parameter across individuals, this application of the model is able to account both for the data of the majority of subjects, who experienced the aftereffect as opposite in direction to the adapting stimulus, and for those of an anomalous subject, who consistently experienced the aftereffect as being in the same direction as the adapting stimulus.

Adult↗

PubMed1988

Neural mechanisms of absolute tactile localization in monkeys.

Macaca nemestrina monkeys were trained to indicate the location of suprathreshold tactile stimuli delivered to the glabrous skin of either foot. The testing paradigm involved self-initiated trials (a bar press), followed by 10-Hz stimulation at one of six locations (e.g., on the distal phalanx of the second toe on the left foot), providing the opportunity for the animal to press one of six buttons located on a facing panel. The buttons were positioned on a picture of a monkey's feet at locations corresponding to the skin loci that were stimulated on different trials. If the animal first pressed the button corresponding to the position stimulated, liquid reward was delivered; responses to any other button terminated stimulation without reward, requiring initiation of another trial for the opportunity to receive reinforcement. The localization errors for normal monkeys were reliably greater along the mediolateral dimension of the foot than they were proximodistally. For example, stimulation of the tip of toe 4 elicited responses to the button at the tip of toe 2 on 25% of the trials, as compared with only 10% errors between the tip of toe 4 and the pad at the base of toe 4. Following unilateral interruption of the dorsal spinal columns at an upper thoracic level, the capacity for absolute tactile localization was unchanged over months of testing. The greater localization accuracy along the proximodistal axis of the foot remained after dorsal column transection. In order to evaluate neural substrates of localization by monkeys, single-neuron receptive field (RF) sizes and distributions within the first somatosensory (SI) cortex were examined to determine the overlap or separation of the representations of different points on glabrous skin. The sample of neurons that provided the RF data was obtained in previous investigations of unanesthetized, neuromuscularly blocked Macaca fascicularis monkeys. Analysis of RF overlap revealed that greater than 50% of cytoarchitectural area 1 units that responded to stimulation of one digit tip also responded to another digit or to the pad at the base of a digit. These large RFs seem poorly suited to subserve a high degree of spatial localization and are compatible with the frequent localization errors by the monkeys in the behavioral experiments. However, the area 1 RF data do not explain the tendency of these animals to exhibit better localization accuracy along the proximodistal axis than along the mediolateral axis of the volar foot.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Functional role of corticoperipheral loop circuits during voluntary movements in the monkey: a preferential bias theory.

The functional role of the sensory input to the motor cortex in the execution of voluntary movements is still controversial. We have proposed that the input functions by changing the excitability of cortical efferent columns before and during movements (Asanuma and Arissian, 1984). Experiments were performed to support this hypothesis. Monkeys were trained to sit still in a chair and to pick up a food pellet from a food board rotating at a high speed, so that the subjects had to concentrate their efforts to pick up the pellet. Microelectrode recordings were made from pre- and post-central cortical neurons related to hand movement during the pickup task. It was found that neurons in the motor (10%) and in the sensory (5%) cortices started discharging far ahead of actual movement of the hand. EMGs in the target muscles, which were identified by microstimulation at the recording sites, revealed that some muscles changed their tone during these premovement discharges, although there were no visible movements of the hand. Section of the dorsal columns abolished the premovement discharges and also produced retardation of motor skills. The results supported the hypothesis that circulation of impulses between the cortical efferent columns and the periphery before the movement plays an important role in the execution of skilled movements.

Animals↗

PubMed1982

Pattern of projection and physiological properties of cortico-cortical connections from the posterior bank of the ansate sulcus to the motor cortex, area 4 gamma, in the cat.

The physiological properties of neurons lying along the posterior bank of the ansate sulcus and the projection of these neurons to area 4 gamma of the motor cortex of the cat were studied and the following results were obtained: (1) Short latency antidromic responses were recorded from neurons along the medial-lateral bank of the posterior ansate sulcus following intracortical microstimulation (ICMS) delivered to motor cortex, area 4 gamma. (2) The posterior ansate region projects topographically to the motor cortex. Neurons in the most medial part of the ansate region project to the medial part of 4 gamma, while neurons in the central and lateral parts of the ansate region project to the more lateral parts of area 4 gamma. (3) In 33 cases, receptive field information was available for both the antidromically activated ansate neuron and from neurons around the stimulating site in 4 gamma. In 58% of the cases, both cortical sites received afferent input from within the same part of the periphery. (4) Afferent input to the motor cortex was examined following combined ablations of the primary somatosensory cortex (SI) and third somatosensory cortex (SIII) including all of area 5. We conclude that the integrity of these cortical regions is not necessary for afferent input to reach the motor cortex.

Afferent Pathways↗

PubMed1982

Physiological properties and pattern of projection of cortico-cortical connections from the anterior bank of the ansate sulcus to the motor cortex, area 4 gamma, in the cat.

The physiological properties of neurons in the postsigmoid gyrus lying along the anterior bank of the ansate sulcus and the pattern of projection of these neurons to the motor cortex, area 4 gamma, were investigated in the cat and the following results were obtained. (1) Neurons lying along the anterior bank of the ansate sulcus receive somatotopically organized afferent input from the skin and deep structures on the contralateral side of the body. (2) Short latency antidromic responses were recorded from all regions along the bank of the sulcus following intra-cortical microstimulation (ICMS) of area 4 gamma. (3) The projection of neurons to area 4 gamma was topographically organized. Neurons in the lateral portions projected to more lateral parts of 4 gamma, whereas neurons in the medial region of the postsigmoid gyrus sent axons to the more medial regions of the motor cortex. (4) In 50 cases, receptive fields were recorded from both the antidromically identified postsigmoid gyrus neuron and from neurons around the activation site in area 4 gamma. In 62% of these instances, both cortical sites received afferent input from within the same part of the periphery.

Animals↗

PubMedDate not supplied

Spatial organization of the peripheral input to area 1 cell columns. I. The detection of 'segregates'.

Extracellular single neuron recording methods are used to study the RFs of neurons comprising area 1 cell columns in unanesthetized Macaca fascicularis monkeys. The RF data obtained in approximately radial microelectrode penetrations demonstrate that the RFs of neurons located within the same area 1 cell columns can differ strikingly, and that it is common for neighboring neurons to possess RFs differing greatly in size or configuration. However, the RF variations detected within a typical area 1 cell mini-column (single cell radial column) appear to be substantially less than the variations observed for nearby neurons lying in different minicolumns. The RF data obtained from arrays of penetrations suggest that the skin representation in the forelimb region of area 1 is organized in a discontinuous, step-like fashion: as a mosaic of discrete 600 micron wide radial cell columns--segregates. Although the RFs of neurons of a segregate can vary substantially in size and configuration, they all share in common a single small area on the skin. The boundaries of a segregate can be mapped precisely because, unlike the situation for neurons located within the same segregate, some of the neurons located on opposite sides of a segregate boundary (belonging to different segregates) have non-overlapping RFs. Furthermore, it appears that within any given segregate there is no systematic shift in RF location as the electrode advances through a sequence of minicolumns. Systematic RF shifts occurred only when the electrode traversed the boundary between neighboring segregates.

Animals↗

PubMedDate not supplied

Spatial organization of the peripheral input to area 1 cell columns. II. The forelimb representation achieved by a mosaic of segregates.

The view (advanced in the previous paper) that the topographic organization in the forelimb region of area 1 of Macaca fascicularis monkeys should be regarded as a mosaic of discrete units--segregates--is evaluated. It is found that in all cortical layers the RFs sampled within a single segregate possess a wide variety of sizes and configurations, and occupy a wide variety of positions on the skin relative to the segregate RF center (the latter is a small skin area common to RFs of all neurons in the segregate). This within-segregate RF variability is structured so that the position of RFs of neurons sampled from different sectors of a segregate exhibits little, if any, systematic shift. The skin area that provides sensory input to any given area 1 segregate (estimated by the aggregate of the RFs sampled from that segregate) is extensive. This 'segregate RF', however, is not homogenous: i.e. central regions of the segregate RF are included in the RFs of a higher fraction of the neurons in the segregate than are peripheral regions. Segregate RFs appear particularly extensive when their size is compared with a relatively small shift in skin position that takes place when one shifts from one segregate to the next. Consequently, the skin areas that provide the sensory inputs to neighboring segregates overlap to a very large degree; and even fairly remote segregates in area 1 can receive a substantial common input. The arrangement of segregate RFs in area 1 is, in general, somatotopic. Nevertheless, the local relationships that are obtained among different segregates can deviate significantly from a strictly somatotopic pattern. The area 1 topographic organization detected in this study appears to differ substantially from that described by other investigators. A more detailed analysis suggests that most of the major differences between this and the previous descriptions of area 1 organization may largely be attributable to the different experimental conditions employed, and that the results of this study and those described by workers using different mapping methods are, in fact, generally compatible. Finally, it is suggested that the mosaic pattern of the topographic organization detected in area 1 may reflect the bundled nature of its afferent input.

Animals↗

PubMedDate not supplied

Minicolumnar activation patterns in cat and monkey SI cortex.

The distribution of stimulus-evoked 14C-2-deoxyglucose (2DG) labeling in primary somatosensory cortex (SI) of monkey (Macaca fascicularis) and cat was investigated. Reconstructions of the global pattern of labeling reveal that discrete skin stimuli evoke activity within an extensive region of SI, and that the activation pattern typically consists of multiple, elongated regions of above-background labeling ("modules," typically 0.5-1.0 mm wide, and 1-4 mm long). Evidence obtained using recently developed methods (Tommerdahl, 1989) for quantitative analysis of 2DG activity patterns is shown to be consistent with the idea (Whitsel et al., 1991) that SI modules typically are bounded by zones dominated by stimulus-evoked inhibition. The labeling pattern within individual 2DG modules in SI of both cats and monkeys is analyzed quantitatively (in the frequency domain). Within-module spatial activation patterns are demonstrated to be periodic, consisting of radially oriented profiles of above-background labeling separated from each other by less strongly labeled radial profiles. The spectral characteristics of within-module 2DG labeling change systematically with location along the module's long axis: spatial frequencies between 18 and 35 cycles/mm are prominent in the labeling that occupies both the middle and upper layers at central locations in the module, but are a less obvious component of the labeling in both the middle and upper layers at locations remote to the module center. Since the radially oriented periodic variation both (1) in 2DG labeling in regions of SI outside modules and (2) in optical density in images of Nissl-stained sections of SI consists predominantly of spatial frequencies in the range of 18-35 cycles/mm, it is concluded that the radial profiles of labeling within individual 2DG modules correspond to groupings of minicolumns distinguishable from their neighbors on the basis of labeling intensity. The findings raise the possibility that highly structured, within-module spatial patterns of SI minicolumnar activation encode information about the physical properties of tactile stimuli.

Animals↗

PubMedDate not supplied

Effects of spinal dorsal column transection on the response of monkey anterior parietal cortex to repetitive skin stimulation.

The pattern of 14C-2-deoxyglucose (2DG) labeling in anterior parietal cortex was evaluated in three groups of experimental subjects: (1) subjects in which all spinal pathways projecting at short latency to the contralateral hemisphere were intact, (2) subjects with either unilateral or bilateral transection of the dorsal column pathway, and (3) subjects in whom a two-stage tractotomy (dorsal column isolation) restricted short-latency mechanoreceptor drive to that conveyed via the dorsal column pathway. Macaca fascicularis and Macaca arctoides monkeys were studied. When the spinal cord pathways projecting at short latency to contralateral anterior parietal cortex were intact, controlled vibrotactile or skin brushing stimuli evoked one or, more rarely, several loci of maximal 2DG uptake (typically 1.5-2.5 mm in diameter) in the topographically appropriate location(s) within area 3b and/or area 1. The labeling at each locus of maximal 2DG uptake extended continuously across layers II-VI. Each locus of maximal 2DG uptake was bordered on one or more sides by irregularly shaped zones of below-background 2DG uptake that could extend without interruption from area 3b into area 3a, and/or from area 1 into area 2. In the absence of skin stimulation, little or no above-background 2DG uptake occurred at any locus within areas 3b and 1 of subjects in which the dorsal column pathway on the opposite side of the spinal cord was intact. In subjects with a complete transection of the spinal dorsal column the global 2DG pattern evoked by a repetitive skin stimulus in contralateral anterior parietal cortex was a near mirror image of the pattern evoked by the same stimulus in intact subjects. In the absence of the dorsal column path, neither 10-25 Hz vibrotactile nor brushing stimulation evoked above-background uptake at the topographically appropriate location(s) within contralateral area 3b and/or area 1. Instead, a prominent region of below-background 2DG uptake occupied the topographically appropriate location in area 3b and/or area 1, and the region of suppressed 2DG uptake was bounded by one or more regions of above-background 2DG uptake that extended from areas 3b or 1 into area 3a and/or into area 2. When a two-stage spinal tractotomy prevented stimulus-evoked short-latency input from reaching contralateral anterior parietal cortex via pathways other than the dorsal column, the 2DG activity patterns evoked in contralateral cortex by either brushing or vibrotactile stimuli were similar to the patterns obtained when the somatosensory pathways on the opposite side of the spinal cord were intact. A neural network model was developed to evaluate the hypothesis that the observed cortical effects of dorsal column transection might be attributable, at least in part, to inhibitory interactions among anterior parietal cortical regions that receive their principal input from different spinal cord pathways. The model incorporated known features of (1) the cortical projection of spinal somatosensory pathways, (2) anterior parietal intrinsic and long-distance horizontal connectivity, and (3) certain neurotransmitter/receptor systems characteristic of sensory neocortex. Simulations of the model network provided results consistent with the idea that repetitive skin stimuli evoke maladaptive, time-dependent corticocortical interactions within anterior parietal cortex contralateral to a dorsal column lesion. The observations indicate that corticocortical interactions account for the (1) near mirror-image pattern (relative to the normal Mexican hat-like pattern) of anterior parietal stimulus-evoked 2DG uptake observed in subjects with a dorsal column lesion, (2) unusual time-dependent response properties of individual area 3b and 1 neurons or neuron populations deprived of dorsal column input (Dreyer et al., 1974; Vierck et al., 1990a; Makous and Vierck, 1994), and (3) abnormal time-dependent characteristics of tactile perception in monkeys with dorsal colum

Acoustic Stimulation↗