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V B Mountcastle

Publications and source records attributed to V B Mountcastle.

33 records · Page 2Linked to original sources
PubMed1975

Capacities of humans and monkeys to discriminate vibratory stimuli of different frequency and amplitude: a correlation between neural events and psychological measurements.

The capacities of monkeys and humans to discriminate between mechanical sinusoids differing in amplitude or frequency were measured in a two-alternative, forced-choice task. The difference limen for amplitude discrimination for both species remained constant near 10% of the standard amplitude over the range of 17-30 dB, relative to detection threshold. Equal subjective intensity curves in the 20-40 Hz range were determined at 20 and 29 dB, relative to detection threshold. These curves followed the threshold curve and were identical for the two species. The difference limen for frequency discrimination averaged 1.8 Hz for humans and 2.7 Hz for monkeys; the range of values for the two species overlapped nearly completely. The small sizes of these difference limens indicate, we believe, the capacity of highly trained individuals of either species to ascertain small differences in the temporal order of somesthetic stimuli and of the neural events evoked by them. In one series of experiments we demonstrated that subjects of both species possess two threshold for two different aspects of flutter-vibration which are displaced from each other along the intensive continuum. For either species, the minimum level of stimulus amplitude required for threshold frequency discrimination is about 8 dB above that sufficient for detection. This difference in amplitude is called the atonal interval and matches that observed between absolute and tuning thresholds for quickly adapting, mechanoreceptor afferents (the Meissner afferents) which innervate the glabrous skin of the monkey hand. These and previous findings have permitted a number of direct correlations between behavioral and neural events as regards the sense of flutter. The neural codes for the intensity and frequency of flutter appear to be different. The capacity to detect the presence of a mechanical sinusoid and the capacity to judge its subjective intensity are likely to depend on criterion levels of activity in the total population of Meissner afferents, the former on the appearance of any activity (absolute threshold) in a small population of the most sensitive of these fibers and the latter on the overall size of the active population of neuronal elements at each level of amplitude. The total activity in the relevant neural population elicited by sinusoids of increasing amplitude defines a prothetic continuum along which subjects can judge the magnitude of sensation..

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PubMed1975

Posterior parietal association cortex of the monkey: command functions for operations within extrapersonal space.

Experiments were made on the posterior parietal association cortical areas 5 and in 17 hemispheres of 11 monkeys, 6 M. mulatta and 5 M. arctoides. The electrical signs of the activity of single cortical cells were recorded with microelectrodes in waking animals as they carried out certain behavioral acts in response to a series of sensory cues. The behavioral paradigms were one for detection alone, and a second for detection plus projection of the arm to contact a stationary or moving target placed at arm's length. Of the 125 microelectrode penetrations made, 1,451 neurons were identified in terms of the correlation of their activity with the behavioral acts and their sensitivity or lack of it to sensory stimuli delivered passively; 180 were studied quantitatively. The locations of cortical neurons were identified in serial sections; 94 penetrations and 1,058 neurons were located with certainty. About two-thirds of the neurons of area 5 were activated by passive rotation of the limbs at their joints; of these, 82% were related to single, contralateral joints, 10% to two or more contralateral joints, 6% to ipsilateral, and 2% to joints on both sides of the body. A few of the latter were active during complex bodily postures. A large proportion of area 5 neurons were relatively insensitive to passive joint rotations, as compared with similar neurons of the postcentral gyrus, but were driven to high rates of discharge when the same joint was rotated during an active movement of the animal...

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PubMed1968

Neuronal coding by cortical cells of the frequency of oscillating peripheral stimuli.

One class of neurons in the somatic sensory cortex of unanesthetized monkeys is rhythmically entrained by sinusoidal mechanical stimulation of the skin of the hand at low frequencies. A second class, which is linked to Pacinian afferents, increases its rate of discharge in response to high-frequency peripheral stimuli but is not entrained. The vibratory sense is served by two distinct classes of cortical cells. The code for the group sensitive to low-frequency stimuli is the temporal order of impulses; for the high-frequency group the code is the labeled line.

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PubMed1967

Neural basis of the sense of flutter-vibration.

Comparison of human detection thresholds for oscillatory movement of the skin of the hand with response properties of first-order myelinated mechanoreceptive afferents from the monkey's hand, activated in an identical stimulus pattern, indicates that flutter-vibration is a dual form of mechanical sensibility, served peripherally by two different sets of fibers.

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PubMedDate not supplied

Selective output-discriminative signals in the motor cortex of waking monkeys.

Monkeys and humans have similar capacities to discriminate between the frequencies of mechanical sinusoids delivered to the glabrous skin of their hands. Combined psychophysical-electrophysiological experiments in monkeys discriminating in the range of flutter provided evidence that this capacity depends upon differences in the cycle lengths in the sets of periodically entrained activity, evoked by the stimuli discriminated, in neurons of areas 3b and 1 of the (sensory) hemisphere opposite the stimulated hand. Identical experiments have now been made, in similarly trained and discriminating monkeys, in the motor cortex (area 4) of the hemisphere opposite the arm projecting selectively to one of two targets, to indicate discrimination (five hemispheres, 1137 neurons studied). We observed a selective signal of the upcoming correct discrimination in about 25% of the neurons of area 4 active in the task. The neuronal discharge occurs selectively for stimuli either lower or higher in frequency than that of the base stimulus, and commonly begins within 200-300 msec after onset of the comparison stimulus. These neuronal discharges are aperiodic, with no sign of the stimulus frequencies. EMG recording during performance of the discrimination showed that the muscles of the arm opposite the side of recording were silent during the period of stimulus presentations. Recordings during trials in which the animal made errors showed most commonly that the output of the discrimination operation was itself in error, followed by an appropriate arm projection to the wrong target. We interpret the selective response during the comparison stimulus to be a postdiscrimination signal projected transcallosally from the sensory hemisphere to the motor area of the hemisphere controlling the responding arm. We obtained no evidence that the discrimination operation is localized to any particular area, and we surmise it to occur in the dynamic activity within the distributed system linking the sensory cortex of one hemisphere and the motor cortex of the other. One-third of the neurons of the motor cortex responded to indentation of the skin of the ipsilateral hand, at trial onset. These responses varied from those closely linked to that sensory stimulus to those linked to the upcoming movement of the contralateral hand. These onset responses did not occur when similar sequences of mechanical stimuli were delivered to alert but idling monkeys.

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