Direct visuomotor transformations for reaching (Buneo et al.) 협동과정 뇌과학 김은영

① Retinal reference frame ▽ ② The brain computes the target position with respect to the hand ▽ ③ Determining the muscle contraction (Batista, 1999)

Direct transformation : Subtracting the position of the hand from the position of the target directly, using eye centered coordinate Indirect transformation : Transforming target location from eye- to head- to body-centered coordinates and then subtracting the body centered position of the hand

(Batista et al., 1999) rr Eye centered coordinate (area MIP neuron) The reach plan that generates the largest response is always the one directly below the eyes. ( Duhamel et al., 1997) Head centered coordinate (area VIP neuron) Single neuron data for visual receptive filed mapping in which the RF remains in the same spatial location irrespective of eye position.

(Graziano et al., 1994) hand centered coordinate (premotor cortex) When the arm is moved to the left, the response filed moves along with it. A, B, C—different eye fixation ⅠⅡⅢⅣ -stimulus trajectory

Experiment Procedure 1)The illumination of both a red and a green LED. The red LED – gaze/ the green LED-hand. 2) A green (target) LED at another location was then briefly illuminated (300 ms duration). 3) a delay period of 600–1,000 ms 4) The LEDs instructing the initial hand location and fixation point were turned off. The animal reached to the remembered location of the target in complete darkness while maintaining fixation. Recording site AREA5 : a subdivision of the PPC that projects directly to cortical and subcortical motor structures

Activity similarity: when target locations were identical in 1)Hand centered coordinate? NO Between conditions 1 and 2 2) Both hand and body centered coordinate? NO Between conditions 3 and 4 3) Both hand and eye coordinates? MAYBE Between conditions 1 and 4 Between conditions 2 and 3 Experiment Ⅰ

* area 5 activity was best correlated when target locations were identical in both eye and hand coordinates

The responses of an idealized neuron coding target location in - Eye coordinates (panels a, b) - Hand coordinates (panel d) - Both eye and hand coordinates (panel c)  reflecting 'compromise‘ between the eye and hand reference frames area 5 (N=89) the distribution of tuning curve shifts : a partial shift  consistent with a simultaneous coding of target location in both eye and hand coordinates

Experiment Ⅱ Condition : 5(target) X 5(initial hand position) Area 5 contours (a largely oblique orientation) resultants  a coding of target location and initial hand location in eye coordinates PRR contour  a coding of target location in eye coordinates. Area Comparison Area 5PRR Contour ResultantBetween eye coordinate and hand coordinate Eye coordinate Condition : 5 (target) X 5 (initial position) Comparison area 5 neurons with the idealized neuron

Neurons in the Area 5 : – employ combined eye centered and hand centered coordinate frame to represent target location. – receive visual, proprioceptive and efferent copy signals. retinal representation ▽ direct transformation ▽ hand centered representation Neurons in the PRR : - ‘gain modulated’ by initial hand location - transformation may be achieved by vectorially subtracting hand location from target location, with both locations represented in eye- centred coordinates.

Reference Batista, A., (2002). Inner space: reference frames. Curr Biol 12, R Duhamel, J.-R., Bremmer, F., BenHamed, S. and Graf, W. (1997). Spatial invariance of visual receptive fields in parietal cortex neurons. Nature 389, 845–848. Graziano, M.S.A., Yap, G.S. and Gross, C.G. (1994). Coding of visual space by premotor neurons. Science 266, 1054–1057.