Analysis of slow cortical potentials preceding self-paced hand movements in the monkey

S47 PROJECTION OF TOOTH P U L P AFFERENTS TO THE SOMATOSENSCRY CORTEX (I AND H I ) O F THE C A T . T ~ ~ A. SUZUKI, Dept. Oral P h y s i o l . , Sch. Dent., Iwate Med. Univ., Uchimaru, Morioka 020. The unit activities elicited by electric~.l stimuiation of the tooth pulp of the canines and m o l a r s w e r e r e c o r d e d in s o m a t o s e n s o r y a r e a I (anterior coro~.al gyrus) 3nd Ill (midd~e part of a n t e r i o r s u p r a s y l v i u s gyru;~). The firing propertie,'; of the si.ngie neurons and the functional organization of the c o l u m n a r s t r u c t u r e s w e r e rna~:lj studio4. The neurons recorded w e r e classified into two types by the~r r e s p o n s e s . Type. I (specific cell) was c h a r a c t e r i z e d by w e l l - s y n c h r o n i z e d initial spikes of short latencies (5-15 reset) and responded only to pulpal stimulus. Type H (non-specific cell) was categorized by the l e s s - s y n c h r o n i z e d initial b u r s t s of long latencies (10-50 m s e c ) followed by prolonged a f t e r - d i s c h a r g e s and resl.~onded not only to pulpal stimulus but also to other t:rpes of stimulation such as m e c h a n i c a l stimuli applied to periodontal t i s s u e , lips~ and facial skin. Although a few exceptional cells w e r e found, most of the specific cells recorded in a r e a I w e r e ~ c i t e d c o n t r a l a t e r a l l y , while the ones in a r e a HI responded bi laterally. In both a r e a s , the c o r t i c a l neurons specific to the p a r t i c u l a r tooth w e r e fotty~u in a column p e r p e n d i c u l a r to the c o r t i c a l surface. The r e s u l t s suggested tlmt this columnar a r r a n g e merit is a common struct-aral c h a r a c t e r i s t i c observable in other s e n s o r y c o ~ e x e s . ANALYSIS Oi~ S L O W C O R T I C A L P O T E .I~r"fIALSP R E C E D I N G S E L F - P A C E D H A N D M O V E M E N T S IN T H E MONKEI'. HISAE G E M B A * , SHUJI H A S H I M O T O * Rnd K A Z U O SASAKI. Dept. Physiol., Inst. Brain Res., Fac. Med., Kyoto Univ., Sakyo-ku, Kyoto 606.

The c o r t i c a l potentials rela'ted to the s e l f - p a c e d "voluntary" hand movement w e r e r e c o r d e d in unanaesthetized, freely moving monkeys with the electrodes implanted chronically on the s u r f a c e and in the depth of the cortex, and analysed by electronic averaging. The s u r f a c e negative - deep positive slew potential changes appeared p r i o r to the movement in ~le motor and p r e m o t o r c o r t i c e s contral~,'.eral to the hand elevar;ng a lever. The potential changes started 800-1500 m s e c before the movement and i n c r e a s ed gradually by about ' 0 0 m s e c before the movement. In re i~:rring to the l a m i n a r field potential ~nalyses of c o r t i c a l evoked potential3 made in our ~ e v i o u s acute e x p e r i m e n t s , m e slow potentials w e r e interpreted to be due to the c u r r e n t of slowly i n c r e a s i n g EPSPs which w e r e gener~tted in superficial p a r t s of c o r t i c a l pyrami~oi neurones via " s u p e r f i c i a l ~halamo.-eortical projections". They would activat, e the n~urones in the motor and p r o motor c o r t i c e s and con*~ibute in initiating the movement. ~ ~,e c o u r s e of m e a s u r e m e a t s for s e v e r a l months, ampli~ade of the slow po~mtial ir~ the p r e m o t o r a r e a b e c a m e gradually larger~ while that in the motor a r e a remained at ~Lc e r t a i n value. It is possible that the p r e m o t o r cortex is closely related with acquired, skilled movement.