Functional mapping of the anterior bank of the superior temporal sulcus (STS) of the macaque monkey

$187 MECHANISMS OF THE RESPONSE SELECTIVITIES OF CELLS IN THE MEDIAL SUPERIOR TEMPORAL (MST) AREA OF THE MACAQUE MONKEY KEIJI TANAKA, HIDE-AKI SAITO and YOSHIRO FUKADA NHK Science and Technical Research Laboratories, Kinuta, Setagaya-ku, Tokyo. We have studied response properties of cells in the DSR region of the macaque's MST area, using monkeys (M. fuscata) anesthetized with N20/O 2 and immobilized with gallamine triethiodide. The DSR region was defined by a clustering of three types of directionally selective cells with large receptive fields; D-cells responding to a straight movement of patterns in the frontoparallel plane, S-cells selectively responding to a straight movement in the depth, and Rf-cells selectively responding to a rotation in the frontoparallel plane (Saito et al., J. Neurosci. 6: 145-157). Since MST receives strong fiber projection from the MT area where the direction of movements within a small receptive field is systematically analyzed, we hypothesized that the receptive fields of D-, S- and Rf-cells were constructed by integrating regional direction signals provided by MT cells. In the present study, we tested this hypothesis especially for the S- and Rf-cells of the Field-type. The Field-type cells respond to a m69ement of a wide textured field, irrespective of the shape of the texture's components, but are~almost insensitive to a movement of a single simple object. Since a size change and rotat&on of a wide textured field contain several factors other than the arrangement of directions of regional movements, i.e., the difference in speed between central and peripheral parts of the stimulus (for both size change and rotation), the size change of individual components of the texture (for size change only) and the accerelation of movements toward the center (for rotation only), it is possible that these non-directional cues are used to make up the selectivities of the Field-type cells. We prepared artificial motion patterns consisting of four quadrants in which dots moved straight in parallel in each quadrant. The movements in each quadrant were directed so that the combination of the movements in four quadrants simulates either radially arranged movements of dots which occur when the dot pattern changes its size or circularly arranged movements which occur when the ~at~ern rotates. Although the motion patterns did not contain the non-directional cues contained in the real size change or rotation, the S- and Rf-cells responded to them as strongly as to the real size hhange or rotation of the dot pattern. We, therefore, conclude that (i) appropriate arrangement of directions of regional movements + (2) wide extent of the movements at a moment are enough for the activation of the Field-type S- and Rf-cells.

FUNCTIONAL MAPPING THE MACAQUE MONKEY

OF THE ANTERIOR

BANK OF THE

SUPERIOR

TEMPORAL

SULCUS

(STS) O F

K A Z U O H I K O S A K A * , M A S A O Y U K I E * , E I I C H I IWAI, H I D E - A K I S A I T O , K E I J I T A N A K A a n d Y O S H I R O F U K A D A . Dept. of B e h a v . P h y s i o l . , T o k y o M e t r o p o l i t a n Inst. for N e u r o s c i . , F u c h u , T o k y o 1 8 3 , a n d N H K Sci. a n d T e c h . R e s . L a b s . , S e t a g a y a , T o k y o 1 5 7 U s i n g m o n k e y s (M. f u s c a t ~ ) a n e s t h e t i z e d w i t h a g a s m i x t u r e of N ~ O : O ~ ( 7 0 : 3 0 ) a n d i m m o b i l i z e d w i t h g a l l a m i n e t r i e t h i o d i d e , s i n g l e u n i t r e c o r d i n g s w e r e m a d e in t h e a n t e r i o r b a n k of t h e c a u d a l h a l f of t h e STS. S y s t e m a t i c r e c o r d i n g s s h o w e d t h a t t h e c o r t e x of t h e a n t e r i o r b a n k c o u l d be d i v i d e d i n t o t h r e e r e g i o n s f r o m m e d i a l to l a t e r a l ; t h e m e d i a l s u p e r i o r t e m p o r a l (MST) a r e a in w h i c h c e l l s w e r e a c t i v a t e d e x c l u s i v e l y by v i s u a l s t i m u l i a n d m o s t l y s h o w e d d i r e c t i o n a l s e l e c t i v i t i e s (Saito et al., J. N e u r o s c i . , 1986); a r e g i o n in w h i c h m o s t c e l l s c o u l d n o t be a c t i v a t e d by v i s u a l , a u d i t o r y o r s o m e s t h e t i c s t i m u l i ; a p o l y s e n s o r y a r e a in w h i c h c e l l s responded to visual, auditory and/or somesthetic stimuli. The polysensory area may be c o n t i n u o u s to t h a t in t h e r o s t r a l S T S ( B r u c e et al., J. N e u r o p h y s i o l . , 1981), b u t t h i s c a u d a l p a r t of t h e p o l y s e n s o r y a r e a is c h a r a c t e r i z e d b y a d o m i n a n c y of c e l l s r e s p o n d i n g to v i s u a l a n d a u d i t o r y s t i m u l i . O u t of 100 c e l l s r e c o r d e d in t h i s a r e a , 43 w e r e u n i m o d a l (20 v i s u a l , 20 a u d i t o r y a n d 3 s o m e s t h e t i c c e l l s ) , 19 w e r e b i m o d a l (15 v i s u a l + a u d i t o r y , 2 visual+somesthetic and 2 auditory+somesthetic c e l l s ) , 4 w e r e t r i m o d a l , a n d t h e r e s t (34) w e r e u n r e s p o n s i v e to t h e s t i m u l i of t h e t h r e e m o d a l i t i e s . V i s u a l r e c e p t i v e f i e l d s w e r e l a r g e (mean size, 6 0 ° x 6 0 °) a n d m o s t c e l l s h a d s e l e c t i v i t y f o r d i r e c t i o n of m o t i o n . A u d i t o r y r e s p o n s e s , w h i c h c o u l d be elicited by various sounds including pure tones, white noise, human voices and c l a p p i n g h a n d s , w e r e s e n s i t i v e to t h e p o s i t i o n of a s o u n d s o u r c e in space. F o r s o m e of v i s u a l + a u d i t o r y c e l l s r e c e p t i v e f i e l d s f o r t h e t w o m o d a l i t i e s o v e r l a p p e d l a r g e l y . T h e a u d i t o r y s o u r c e h a d to m o v e in a p a t i c u l a r d i r e c t i o n in s p a c e f o r s t r o n g a c t i v a t i o n of s o m e c e l l s , a n d t h i s d i r e c t i o n of m o t i o n c o i n c i d e d w i t h t h e p r e f e r r e d d i r e c t i o n of v i s u a l r e s p o n s e s . S o m e s t h e t i c r e c e p t i v e f i e l d s w e r e l a r g e , u s u a l l y i n c l u d i n g the w h o l e b a c k of t h e body, a n d m o s t c e l l s w e r e a c t i v a t e d by a l i g h t t o u c h on t h e s k i n o r b y b e n d i n g of t h e h a i r s .