554 BRAIN MECHANISMS AND LEARNING 



Olds. Dr Buser mentioned that he could tell from the oscilloscope tracing that a 

 response was abortive. I didn't sec quite which was the characteristics of the tracing 

 that indicated that a response was an abortive one. 



Buser: As recording evoked potentials to the signal stimulus trom the motor 

 cortex, it appeared to us that a normal lever pressing movement was preceded by 

 an electrocortical activation as well as by an apparent 'suppression' of these frontal 

 evoked responses. A further and rather surprising observation was that inefficient, 

 or 'abortive' movements, though being also preceded by a slight desynchroniza- 

 tion, were not, in most of the cases, accompanied by a suppression of motor evoked 

 responses. 



Segundo. Dr Buser, variotis groups in the Institut Marey have explored the 

 cortical and subcortical distribution of sensory volleys extensively. Could you give 

 us an idea as to what pathways visual and acoustic impulses may follow to reach the 

 motor cortex. 



Buser. The precise route for light and sound onto the motor cortex still remains 

 a matter for discussion. 



We have, until now, very little to add to opinions expressed by others, suggest- 

 ing a role of the pretectal area (Wall et ah, 1953) or reticular formation (Hunter and 

 higvar, 1955). Nevertheless, some of our recent results seem to indicate that a small 

 area in the posterior thalamus — close to both suprageniculate and magnocellular 

 fraction of medial geniculate, as well as centre median could play an important 

 role in transmission of light impulses to the motor cortex (Buser and Bruner, un- 

 published). 



JouvET. Did you record simultaneously in the visual cortex and the reticular 

 formation? 



Buser. Not yet. 



Garcia-Austt. What differences exist, if any, between the latencies and shape of 

 potentials evoked by visual stimuli on the motor cortex on one hand and on the 

 visual cortex on the other >. 



Buser. In brief, evoked responses to light, recorded from the sensory motor 

 cortex, in chronic animals, sho\v following characteristics: latency about three 

 times that of the primary response, longer duration and smooth contours (no 

 sharp surface positive component); smaller amplitude (one-half to one-third). 



