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ROBERT M. BENJAMIN 



contrasts interspike interval plots with the more familiar frequency plots. 

 These are examples of " nociceptive " unit responses which are particularly 

 well suited to illustrate the characteristics of dot patterns. 



At the upper left is a frequency plot of a common, slowly, adapting unit. 

 It has no spontaneous activity. When the stimulus is applied (black bar), 

 the frequency of spikes increases rapidly to a maximum and then slowly 

 decreases as the stimulus continues over 60 sec. At the termination of the 



Fig. 6. Comparison of frequency plots and interspike interval dot patterns for 

 two single neurons. See text for explanation. 



Stimulus, the frequency of impulses again returns to zero. Below is an 

 interspike interval plot of the same response constructed on the same time 

 scale. The ordinate, however, measures the interspike intervals, that is, 

 the time between two successive spikes. Each dot represents a spike and its 

 distance from the abscissa (0 msec) indicates the amount of time in msec, 

 since the previous spike. A short time corresponds to high frequency, a 

 longer time, to a lower frequency. This plot is photographed from taped 

 data being played back to an oscilloscope which is sweeping up the ordinate, 

 so to speak. The circuitry is arranged so that the first spike triggers the 

 sweep, in this example 500 msec in duration. The second spike does 

 several things ; it intensifies the beam to produce a dot, immediately 

 returns the sweep to zero, and then triggers another sweep. The next spike 

 produces another dot marking the second interval, resets the sweep and 

 so on. These dots are photographed on very slowly moving film which 

 spreads them out along the abscissa. Although it is not apparent, there is 



