Tactile Discrimination Task is not Disturbed by Thalamic Electrical
Stimulation

Arash Fazl
Department of Cognitive and Neural Systems
Boston University

The major pathway of human somatosensation passes through the
Ventrocaudal (Vc) nucleus of the thalamus. We tested the effect of
direct electrical stimulation of the Vc nucleus on tactile
discrimination in five Parkinson patients undergoing stereotactic
thalamotomy. Raised gratings with lines 3, 4, or 6 mm apart were used.
Patients had to actively touch test patterns placed in the hand
contralateral to the thalamus under operation and compare it with a
reference 3mm grating held continuously in their other hand. Their
performance was best for 6mm, followed by 3mm and then by 4mm patterns
regardless of electrical stimulation. Under Vc stimulation, patients
recognized the 4 mm gratings slightly better. This might be explained
either by the nature of thalamocortical interaction, which makes it
resistant to external noise or involvement of other pathways that
circumvent the effect of thalamic stimulation.