Abstract
Purpose: :
To map the visual receptive fields of neurons in the medulla of the Limulus brain.
Methods: :
To gain access to the brain we opened a hole on the dorsal carapace of the prosoma and removed overlying tissue and organs. After desheathing the brain, we penetrated neurons in the medulla with a glass microelectrode. We classified cells with full eye and single ommatidial illumination, mapped their receptive fields with pattern stimuli and recorded responses to underwater video scenes.
Results: :
Responses of medullar cells can be classified into "simple" and "complex" types. Simple type "ON" and "OFF" responses are similar to those of vertebrate ganglion cells. "ON" response type can have excitatory receptive fields ranging from 6 to 40 degrees with no detectable surround components. Receptive fields of simple type "OFF" cells have not yet been mapped. Complex cells include "ON", "OFF" and "sustained" and "transient inhibitory" responses. Their receptive fields can be highly complex with noncontiguous regions of excitation and inhibition.
Conclusions: :
We have previously reported that responses from medullar cells are similar to those recorded from retinal ganglion cells i.e. sustained and transient "ON" and "OFF" cells. Depending on response type, receptive fields can be simple or highly complex indicating several levels of visual processing in the medullar region of the Limulus brain.
Keywords: electrophysiology: non-clinical