TOUCH AND KINESTHESIS 



407 



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16 M 12 10 8 6 4 2 I 3 5 7 9 II 

 LOCATION OF THE STIMULATED POINT 



13 15 



FIG. 9. Graph relating the average number ot impulses 

 discharged per response to the position of the stimulus at 

 several points located in and around the receptive field. Inset 

 drawing on the left indicates the location of the receptive field; 

 inset drawing on right the positions of the stimulated points. 

 Electrical stimulus of the same strength is delivered through a 

 pair of needle electrodes thrust into the skin. The same unit 

 located in the ventrobasal complex of the thalamus is respond- 

 ing throughout. Graph is based on 1208 responses. Cat under 

 deep pentobarbital anesthesia. [From Mountcastle, V. B. & 

 J. E. Rose, unpublished observations.] 



illustrates the first type, shown here for a thalamic cell. 

 Several characteristic phenomena for this type of 

 response are as follows: 



a) Equilibration. The neuron follows the stiinulus 

 rate beat-for-beat to a certain level, usually in the 

 range of 30 to 70 per sec. When trains of stintuli at 

 higher rates are delivered, the neuron continues to 

 respond at about the same overall rate. There is no 

 desynchronization, however, for each response occurs 

 in a fixed and definite relation to a particularstimulus. 

 The equilibration occurs JDecause some stimuli ran- 

 domly distributed throughout the train fail to evoke 

 responses. 



6) Early silent period. The records of figure 1 2 show 

 that while the first stimulus elicits a response, the next 

 few (i.e. numbers 2, 3, 4, 5, etc., in fig. 12) may be 

 ineffectual. The succeeding stimuli, however, once 

 again become effective. This early silent period is of 

 about the same duration as the unresponsive time of 



the system, as measured in the two stimulus experi- 

 ment under the saine experimental conditions. The 

 important point is that the presentation of trains of 

 stimuli ' recruits excitabilitv' so that the svstem 



FIG. 10. Shifts in the number of impulses per response and 

 changes in the latent periods with increased strength of the 

 peripheral stimulus for three units located at successively higher 

 synaptic regions of the medial lemniscal system of the cat. 

 Stimulus strength increases in each column from above down- 

 ward. Time lines for all columns, 1000 cycles per sec. B: Dis- 

 charges of a single neuron of the cuneate nucleus evoked by 

 stimulation of the ipsilateral radial cutaneous nerve. Note the 

 shift in latencies and the increase in the number of spikes with 

 increase in stimulus strength. The strength of the stimulus is 

 indicated by the traces at the extreme left {A} which show 

 increases in the size of the compound action potential in the 

 radial nerve. [From Amassian & DeVito (15).] C: Increase in 

 number of impulses of the early repetitive response of a single 

 neuron of the ventrobasal thalamic complex evoked by in- 

 creasingly stronger electrical stimuli (ai) delivered to the skin of 

 the contralateral first digit of the forepaw. Traces show the 

 modal number of the discharge train at each stimulus strength 

 and a latency which is close to the mean latency at this strength. 

 [From Rose & Mountcastle (208).] D: A similar series for a 

 neuron located in the first som.atic cortical field. Electrical 

 stimulation of the skin of the contralateral foreleg. Each trace 

 shows again the modal number for the discharge train at given 

 strength of the stimulus and the latency, near to the mean 

 latency at this strength. [From Mountcastle el a!. (183).] 



