INHIBITORY INTERACTION IN THE RETINA 



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_] I I J I 



5 mm. 



and __ 

 A ■ 



A I 

 alone. 



Fig. 13. Oscillograms of the electrical activity of two optic nerve fibers, showing 

 disinhibition. In each record the lower oscillographic trace records the discharge 

 of impulses from ommatidium A, stimulated by a spot of light confined to its 

 facet. The upper trace records the activity of ommatidium B, stimulated by a spot 

 of light centered on its facet, but which also illuminated approximately eight or 

 ten ommatidia in addition to B. A third spot of light, C, was directed on to a region 

 of the eye more distant from A than from B (the geometrical configuration of the 

 pattern of illumination is sketched above). Exposure of C was signalled by the 

 upward offset of the upper trace. (Lower record) — Activity of ommatidium A 

 in the absence of illumination on B, showing that illumination of C had no per- 

 ceptible etTect under this condition. Upper record: activity of ommatidia A and B 

 together, showing (i) lower frequency of discharge of A (as compared with lower 

 record) resulting from activity of B, and (ii) effect of illumination of C, causing a 

 drop in frequency of discharge of B and comitantly an increase in the frequency 

 of discharge of A, as A was partially released from the inhibition exerted by B. Time 

 in I sec. The black band above the time marks is the signal of the illumination of 

 A and B, thin when A was shining alone, thick when A and B were shining 

 together. (From Hartline and Ratlift", 1957.) 



These quantitative measurements compel us to accept the principle of 

 mutual interdependence of receptor responses. Thus it appears that while 

 the strength of the inhibitory influence generated by any receptor is deter- 

 mined by its output, the locus at which this influence is exerted on a neigh- 

 boring receptor is at, or ahead of, the point at which the neighbor's output is 

 determined. The inhibitory influences are transmitted reciprocally and in a 

 sense recurrently over the plexus pathways. In this respect the inhibition in 

 the Limulus eye is reminiscent of the recurrent (Renshaw) inhibition familiar 

 in the physiology of spinal reflexes and discussed elsewhere in this sym- 

 posium by Professor Granit. We note in this connection that it has been 

 suggested that recurrent facilitation is a disinhibition which enhances reflex 

 discharge by the removal of tonic inhibitory activity (Wilson el al., 1960). 



In the eye of Limulus, the quantitative expressions describing the essential 

 properties of the inhibitory interaction have been found to be comparatively 



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