Electrical activity observed in guinea-pig olfactory cortex maintained in vitro.

1. Electrical recordings were made from a preparation of guinea-pig olfactory cortex maintained in vitro.2. The response of the prepiriform area to a volley delivered to the lateral olfactory tract comprised a sharp negative deflexion upon which several positive notches were superimposed followed by a long-duration low-amplitude positive wave.3. Both the negative and positive waves were of maximal amplitude near the top surface of the preparation (the original cortical surface).4. Units recorded at depths of 250-350 mu showed facilitation and latency variation. The latency distribution of these spikes was very similar to that of the positive notches observed on the surface of the slice.5. The surface observed negative waves were rapidly abolished by oxygen lack.6. The negative and positive waves have been tentatively identified as the extracellular manifestations of the excitatory post-synaptic potentials (EPSPs) and inhibitory post-synaptic potentials (IPSPs) occurring in the apical dendrites.7. Some spontaneous activity was observed in a proportion of the preparations studied.8. The evidence presented here strongly supports the contention that portions of the mammalian brain may be maintained in a satisfactory functional condition when isolated from the body, provided that they are maintained in a suitable environment. We believe that such preparations will prove very useful for physiological studies of the mammalian brain.