R. HERNANDEZ-PEON AND H. BRUST-CARMONA 



397 



Tactile habituation at the spinal cord in intact cats. The participation of the 

 various levels of the central nervous system (including the lowest one) in 

 habituation can be demonstrated only by studying spinal afferent re- 

 sponses which might be modified by the spinal cord itself. 



It IS known that repetition of electrical stimuli applied to the skni 

 results in a significant decrement of the corresponding sweat, respiratory 

 and muscular responses (Seward and Seward, 1934). By local electro- 

 myographic recordings Hagbarth and Kugelbcrg (1958) have recently 

 shown that the abdominal skin reflex also undergoes habituation by 



Fig. 3 

 Habituation of tactile evoked potentials recorded from the lateral column of the spinal cord 

 in an awake freely moving cat. The tactile stmiulus (single cutaneous shock) was regularly 

 repeated at intervals of 10 seconds. 



repetition of the corresponding stimuli. All these observations indicate 

 that like other polysynaptic reflex responses, spinal reflexes induced by 

 tactile stimulation can be diminished in tlie intact organism by a process of 

 habituation. 



Since previous studies have demonstrated that habituation can occur as 

 iar down as the cochlear nucleus (Hernandez-Peon, Jouvet and Scherrer, 

 1957), the retina (Palestini, Davidovich and Hernandez-Peon, 1959), the 

 olfictory bulb (Hernandez-Peon, Alcocer-Cuaron, Lavin and Santibanez 

 1957), and the spinal tifth sensory nucleus (Hernandez-Peon, Miranda and 

 Davidovich, 1959), it seemed likely that afjereiit neuronal habituation would 

 also occur at the spinal level. With the purpose of testing this hypothesis, 



