[Abstract Title]. - Society for Neuroscience

Poster
262. Visually-Guided Reaching II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 262.14/CC28
Topic: D.05.d. Visually guided reaching
Title: Short-latency manual responses of monkey are impaired by lesions in the MST
Authors: *A. TAKEMURA 1,2 , T. OFUJI 3 , N. ABEKAWA 4 , K. KAWANO 5 , H. GOMI 2,4 ;
1 Neurosci Res. Inst., AIST, Tsukuba, Ibaraki, Japan; 2 SHIMOJO Implicit Brain Function Project,
ERATO, JST, Kanagawa, Japan; 3 Grad Sch. of Comprehensive human sci, Univ. of Tsukuba,
Tsukuba, Ibaraki, Japan; 4 NTT Communication Sci. Labs, Atsugi, Kanagawa, Japan; 5 Grad Sch.
of Med, Kyoto Univ., Kyoto, Japan
Abstract: When a sudden drifting motion of a surrounding visual stimulus is given during
reaching movement of an upper limb, the limb trajectory is deviated towards the direction of
motion. This rapid manual response is elicited with an ultra-short latency (~70 ms in monkeys),
termed „Manual Following Response (MFR)‟ (Saijo et al. 2005, Gomi et al. 2006). This
visuomotor response might be functional in quickly adjusting the reaching movement during
self-movements accompanied by visual motion of the background. On the other hand,
unexpected target shifts also elicit another adjustment of ongoing reaching movement with a
short latency (~100 ms in monkeys).
The medial superior temporal (MST) area of the monkey‟s cortex contains a preponderance of
neurons which encode the direction of motion of visual stimuli, including many that respond
selectively to full-field visual motion (optic flow).
In the present study, to determine whether the MST plays a role in eliciting these manual
responses by on-line control mechanisms during reaching, we examined the effects of injecting
muscimol (a GABA agonist) into the left MST of two monkeys. The monkey faced a CRT in a
dark room with its head fixed in the standard stereotaxic position. The CRT was 366 mm in front
of the eyes and the visual stimulus was subtended 62° x 50° along the vertical and horizontal
meridian. The visual stimulus was a pair of vertical sinusoidal grating patterns (anti-phase) of a
fixed contrast (50%). When the monkey pressed the button, a red fixation target appeared in the
center of the CRT. After a random delay, the target color became green, which instructed the
monkey to release the button. The monkey had to release the button and touch the CRT to get a
reward. The size of the reward was inversely proportional to the magnitude of the error to
encourage accurate reaching in the training period.
When we gave the monkey a total of two muscimol injections (10 mg/ml, 4.0 κl total) into the
MST of the left hemisphere, the MFR was abolished one hour after the injections. As for the
other manual response to the target shift, the initial response was decreased substantially