Cortical and subcortical components in the recruiting responses

Abstract

1. 1. Surface negative recruited potentials are reversed in sign by local application of 5 per cent cocaine on the cerebral cortex. 2. 2. After ablation of the whole of the grey matter in a cortical area, the recruited potentials recorded from the underlying white matter are always positive in sign. 3. 3. Surface negative recruited potentials become reversibly positive in sign during the initial phase of the asphyxia. If the latter is prolonged, the positive potentials gradually decrease in size until only stimuli artifacts are recorded. 4. 4. Negative recruiting responses and strychnine “spikes” are abolished by local cocaine and by asphyxia when almost no effect is observed on positive recruited potentials. The latter type of response is thus definitely more resistant to any condition yielding cortical depression. 5. 5. The surface positive wave is due — as others have shown for thalamic specific projection systems — to activity in afferent fibres failing to excite trans-synaptically the cortical neurons. Whenever cortical cells are activated by volleys from medial thalamic structures impinging upon them, a surface negative recruiting response occurs. 6. 6. The gradually increasing cortical response is due to recruitment of thalamic neurons, occurring possibly in the reticular complex. Also the waxing and waning of the recruiting response is due to fluctuation in thalamic excitability. There is no need of postulating the existence of recruiting phenomena and of fluctuations in excitability primarily localized within the cerebral cortex, although it has not been disproved.