Simultaneous optical monitoring of activity of many neurons in invertebrate ganglia using a 124-element photodiode array.

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Abstract
Optical methods for monitoring neuron activity were further developed with the aim of using these methods to study how groups of neurons interact to control behavior. The number of photodetectors was increased from 14 (22) to 124. The results suggest that the apparatus can monitor action potential activity in a few hundred neurons if the cell bodies are large (> 30 .mu.m diameter) and they are fully invaded by the action potential. Pharmacologic effects of the dyes were troublesome. Conditions were found where optical detection could be used to find neurons participating in a behavioral response while simultaneous electrode measurements suggested that there may not have been pharmacologic effects. In experiments where signal averaging could be used, potential changes as small as 1 mV were detected optically. [Subesophageal ganglia of Balanus nubilus, buccal ganglia of Navanax inermis and segmental ganglia of Macrobdella decora and Hirudo medicinalis were used.].