[Interrelations of the emotionally positive and negative areas of the brain in the edible snail].

Fine wire electrodes were surgically implanted in two regions of a snail's brain (Helix aspersa). To receive electrical stimulation of the brain, the tethered snail was required to displace the end of a rod. Self-stimulation delivered to the parietal ganglion resulted in nonrepetition of the operant response, whereas self-stimulation delivered to the mesocerebrum resulted in an increase in response frequency. In neurophysiological experiments it was found that extracellular stimulation of mesocerebrum inhibits spontaneous activity of serotonergic cells modulating avoidance reactions, and decreases synaptic input of a command cell for avoidance behaviour. These findings make possible intracellular investigations of the mechanisms of positive and negative reinforcement.