Visual evoked potentials at hypothalamic and tegmental areas of the upper brain-stem

Abstract

1. 1. One hundred experiments were carried out in twenty-three albino rats with chronically implanted electrodes in the following areas: ventrolateral tegmentum (VLT), posterior lateral hypothalamus (PLH), anterior lateral hypothalamus (ALH), septal area (S), tecto-tegmental area (TT) and the visual cortex (VC). Four to five experiments were repeated in each animal. 2. 2. Photic stimulation was carried out by means of a miniature lamp fastened to the frontonasal bone, the evoked response being summated with a CAT Mnemotron. Recordings were obtained using as reference an intracerebral electrode as well as from pairs of electrodes with a small inter-electrode distance. In two rats with electrodes implanted chronically at VC, PLH and VLT, on both sides, enucleation of one eye was carried out. Photic stimulation tests, during 1–2 h, were performed leaving the animal unrestrained in a wood or red plexiglass box. 3. 3. Photic stimulation provoked a response, preferably in the caudal group of the areas surveyed. Both with the referential and the bipolar recording the response predominated in, or was confined to, the PLH and VLT. On the other hand, the response was absent or showed a very small amplitude at more rostral regions. 4. 4. Changes in wakefulness and sleep provoked modifications in the tegmental and hypothalamic responses; these did not parallel those of the visual cortical response. 5. 5. Enucleation of one eye did not provoke important changes in the characteristics of the response on the side of the preserved eye in PLH and VLT.