Tactile Discrimination Task Not Disturbed by Thalamic Stimulation   (in "Stereotactic and Functional Neurosurgery")

Stereotact Funct Neurosurg 2001;76(1):19-28

Abbassian A.H.¹, Shahzadi S. ^1,2, Afraz S.R. ¹ ,Fazl A. ^1,3 , Moradi F. ^1,3

^1. Department of Epistemology and Cognitive Sciences, School of Intelligent Systems, Institute for Studies in Theoretical Physics and Mathematics, Tehran, Iran.

^2. Neurosurgery Department , Shohada Hospital, Shahid Beheshti University of Medical Sciences. , Tehran, Iran.

^3. Faculty of Medicine, Tehran University of Medical Sciences.

 , Tehran, Iran

 

Abstract

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 can 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.

 

 

 

For the non-medical readers, we studied the effect of electrical stimulation in the sensory thalamus during the stereotactic surgery, wherein the patient is conscious. We found that while the electrode was injecting a large electrical current into the thalamus and the patient had tingling in the corresponding body part, his/her sensation was not impaired and still could tell between our different sensory stimuli, shown above.