Biomedical subjects

D C Bishop

Publications and source records attributed to D C Bishop.

12 recordsLinked to original sources

PubMed2001

The gain of initial somatosensory evoked potentials alters with practice of an accurate motor task.

The gain of somatosensory afferent paths from the lower limb to the cerebral cortex was investigated during the acquisition of one target location during plantar flexion. Sensory gain was measured as the magnitude of somatosensory evoked potentials (SEPs) following electrical stimulation of a peripheral nerve in the lower limb, and was recorded from the scalp. We hypothesized gain attenuation of SEPs from sensory paths serving the limb segment responsible for target acquisition. SEP gain was studied as subjects plantar flexed about the anide to a target that was 15 degrees beyond the occurrence of a cutaneous stimulus (cue) to the lateral border of the foot. The "cue" was either fixed in one location or could appear at one of three positions in space. SEP gain was tested during practice and with task acquisition. Electroencephalographic (EEG) recordings were made of primary and secondary complexes of cortical SEPs from sural and tibial nerve stimulation, with 30-40 samples averaged per subject-condition. Electromyographic (EMG) records were made of soleus muscle H-reflexes and M-waves. Target acquisition was recorded as percent correct hits. The results showed significant attenuation in sural and tibial nerve primary SEPs with task acquisition when the cue was fixed or varied in movement space (P<0.05). Secondary SEPs from tibial nerve followed this pattern. Spinal H-reflexes only attenuated with movement per se. We conclude that the CNS preferentially reduces the cerebral inflow of sensory information once such a motor task has been successfully acquired.

Adult↗

PubMed1999

Temporal properties of attention sharing consequent to disturbed balance.

The time course and extent of attentional shifts associated with compensatory balancing reactions were explored using a novel dual-task paradigm. Seated subjects performed a continuous visuomotor tracking task with the hand while the feet simultaneously balanced an inverted pendulum. The pendulum was randomly perturbed, evoking compensatory balance reactions. Changes in tracking performance were held to reflect attentional shifts. Discrete deviation in visuomotor tracking, typically a pause in tracking, began on average 235 ms after the onset of the balance reaction (TA EMG; average latency 90 ms). Such pauses lasted on average 600 ms, although additional errors in tracking lasted up to 9 s following the perturbation. The findings reveal evidence of dynamic shifts in attention associated with distinct phases of compensatory balance control. The initial phase appears to be triggered automatically, whereas later phases involve varying degrees of attentional resources.

Adult↗

PubMed1997

Simultaneous anterograde labeling of axonal layers from lateral superior olive and dorsal cochlear nucleus in the inferior colliculus of cat.

The laminar organization of the central nucleus of inferior colliculus includes layers of axons that may be important in shaping the responses of neurons. Depending on their source, some layered axons are afferents that are superimposed and terminate on the same postsynaptic neurons, while other layered afferents, such as those from the ipsilateral and contralateral lateral superior olive, terminate side-by-side. The specific pattern of convergence may dictate which populations of axons are presynaptic to layered disc-shaped neurons in the central nucleus. We compared the distribution of afferent axons from the dorsal cochlear nucleus and the lateral superior olive to the contralateral inferior colliculus in the cat. Injection sites in cochlear nucleus and superior olive were physiologically characterized by extracellular recordings of single and multiple units in response to monaural and binaural acoustic stimulation. Two separate injections were made in each case, and both injection sites contained units with overlapping best frequencies. Biotinylated dextran, fluorescent dextran, 3H-leucine, and wheat germ agglutinin conjugated to horseradish peroxidase were used as anterograde tracers. The present results show that layered axons from the dorsal cochlear nucleus and lateral superior olive are superimposed in part of the contralateral central nucleus. Both projections were arranged in rostro-caudally oriented axonal layers that converged in the ventral part of the central nucleus. However, in the dorsal part of the central nucleus, the same layer of axons from the dorsal cochlear nucleus did not terminate with afferents from the lateral superior olive. Within the overlapping layers in the ventral central nucleus, the overlap of axons from the dorsal cochlear nucleus and the lateral superior olive was uniform except for small patches that were usually smaller than the dendritic fields of disc-shaped neurons. These data suggest that the layers may create specific functional zones in the central nucleus of the inferior colliculus. One zone may contain neurons with binaural responses that combine the properties of the inputs from the contralateral lateral superior olive and the dorsal cochlear nucleus. A second zone may contain inputs from the cochlear nucleus but lack those of the lateral superior olive.

Afferent Pathways↗

PubMed1978