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B L Whitsel

Publications and source records attributed to B L Whitsel.

At least 55 records · Page 3Linked to original sources
PubMed1978

Thalamic projections to S-I in macaque monkey.

The organization of thalamic input to functionally characterized zones in primary somatosensory cerebral cortex (S-I) of macaque monkeys (Macaca mulatta) was investigated using the method of labelling by retrograde transport of horseradish peroxidase (HRP). It was found that the cell columns positioned at the posterior margin of the band of cortex representing a given body region receive thalamic input from a posterior level of the ventroposterior thalamic nucleus (VP), and that cell columns at successively more anterior positions within that band receive input from successively more anterior levels of VP. The extreme posterior and anterior margins of the S-I hand, foot and face areas receive input from neuron populations which are not as widely separated in the anteroposterior dimension of VP as the neurons projecting to the extreme anterior and posterior margins of the proximal limb and trunk representations in S-I. These characteristics of the organization of the projections from VP to S-I are consistent with the view that the body representations in VP and S-I have the same connectivity and differential submodality distribution; and with the idea that thalamocortical conncetions only exist between functionally equivalent neuron populations in VP and S-I.

Adaptation, Physiological↗
PubMed1978

Variability in somatosensory cortical neuron discharge: effects on capacity to signal different stimulus conditions using a mean rate code.

1. The present study is based on the demonstration (8, 9) that the relationship between mean interval (MI) and standard deviation (SD) for stimulus-driven activity recorded from SI neurons is well fitted by the linear equation SD = a X MI + b and on the observations that the values of the slope (a) and y intercept (b) parameters of this relationship are independent of stimulus conditions and may vary widely from one neuron to the next (8). 2. A criterion for the discriminability of two different mean firing rates requiring that the mean intervals of their respective interspike interval (ISI) distributions be separated by a fixed interval (expressed in SD units) is developed and, on the basis of this criterion, a graphical display of the capacity of a neuron with a known SD-MI relationship to reflect a change in stimulus conditions with a change in mean firing rate is derived. Using this graphical approach, it is shown that the parameters of the SD-MI relationship for a single neuron determine a range of firing frequencies, within which that neuron exhibits the greatest capacity to signal differences in stimulus conditions using a frequency code. 3. The discrimination criterion is modified to incorporate the changes in the symmetry of the ISI distribution observed to accompany changes in mean firing rate. It is shown that, although the observed symmetry changes do influence the capacity of a cortical neuron to signal a change in stimulus conditions with a change in mean firing rate, they do not alter the range of firing rates (determined by the parameters of the SD-MI relationship) within which the capacity for discrimination is maximal. 4. The maximal number of firing levels that can be distinguished by a somatosensory cortical neuron (using the same discrimination criterion described above) discharging within a specified range of mean frequencies also is demonstrated to depend on the parameters of the linear equation which relates SD to MI. 5. Two approaches based on the t test for differences between two means are developed in an attempt to ascertain the minimum separation of the mean intervals of the ISI distributions necessary for two different mean firing rates to be discriminated with 80% certainty.

Animals↗
PubMed1978

Factors influencing cutaneous directional sensitivity.

The influence of stimulus velocity and traverse length on the ability of human subjects to indicate in which of two opposite directions a brush moved along the skin was determined using a forced choice procedure. Stimulus velocities ranged from 0.75 to 250 cm/sec, and traverse lengths ranged from 0.5 to 6 cm; measurements were made on both the thenar eminence and the preaxial upper arm. Performance was expressed in terms of "critical traverse length" i.e., that traverse length at which, for a given velocity, the subject would correctly identify the direction of brush motion on 75% of the trials. The data indicate that the capacity to identify direction of tactile stimulus motion increases with traverse length and is optimal for velocities between 3 and 25 cm/sec. The overall level of performance was better on the thenar than on the upper arm.

Adult↗
PubMed1978

Representation of moving stimuli by somatosensory neurons.

The findings obtained in neurophysiological and psychophysical investigations using tactile stimuli that move at constant velocity across the skin are reviewed. For certain neurons in the postcentral gyrus of the cerebral cortex (S-I) of macaque monkeys, direction of stimulus motion is a "trigger feature"" i.e., moving tactile stimuli evoke vigorous discharge activity in these neurons only if the stimuli are moved in a particular direction across the receptive field. This directional selectivity is maximal when stimulus velocity is between 5 and 50 cm/sec, and falls off rapidly at lower or higher velocities. The capacity for human subjects to correctly identify the direction of stimulus motion on the skin exhibits a similar dependence on stimulus velocity. The similar effects of velocity on neural and psychophysical measures of directional sensitivity support the idea that direction of stimulus motion on the skin can only be recognized if the moving stimulus optimally activates the group of S-I neurons for which that directions of simulus motion is the trigger feature.

Action Potentials↗
PubMed1975

Representation of head and face in postcentral gyrus of the macaque.

The receptive field and submodality characteristics of individual neurons within the cytoarchitectural and topographic subdivisions of the head and face areas of the postcentral gyrus (SI) were determined with the technique of extracellular recording. Correlation of the single-unit data with the intracortical location of the recording electrode provided a detailed description of the functional organization within each of the several cytoarchitecturally distinct regions contributing to the representation of the head and face in SI. The data indicate that the functional organization of the SI cortex which receives its principal input from trigeminal mechanoreceptors is comparable to the organization within those SI regions which receive their input from the mechanoreceptors of the limbs, trunk, and tail. In each topographic subdivision of the SI cortex 1) a single region in the periphery is represented several times in widely separated locations, each time in a context of different submodalities and peripheral receptive fields; and 2) neurons belonging to the different submodality classes are segregated so that projections from cutaneous afferents terminate mainly in cytoarchitectural area 3 in the adjacent anterior portion of area 1, while projections from the afferents innervating deep tissues terminate mainly in cytoarchitectural area 3a, area 2, and the posterior part of each 1. Although the mechanoreceptor input to SI is segregated according to submodality and the mechanoreceptors from most body regions project to multiple widely separated regions within SI, neurons with receptive fields confined to the ophthalmic division of the trigeminal peripheral innervation field are found within a restricted region of the anterior postcentral gyral crown which is positioned symmetrically about the junction of cytoarchitectural areas 1 and 3. Neurons with receptive fields confined to the maxillary division of the trigeminal innervation field are found within a ring of cortex which a) completely surrounds the representation of the ophthalmic field, and b) includes parts of cytoarchitectural area 2, 1, 3, and 3a. SI neurons with receptive fields restricted to the mandibular division of the trigeminal innervation field occupy the largest portion of the SI face area and form a ring of cortical cell columns which completely surrounds that cortical region which receives its input from the maxillary peripheral innervation field.

Animals↗