A recent study published in the Archives1 attempted to test a speculation of Pavlov's2 concerning the changes in cortical activity that accompany the conditioning process. Pavlov hypothesized that the association between the conditioned stimulus (CS) and the unconditioned stimulus (US) is mediated in the cerebral cortex by a path of excitation between the CS locus and the US locus. During the extinction period, i. e., when the CS is presented alone, the disappearance of the conditioned response (CR) is ascribed to the spread of inhibitory processes in the cortex.
Morrell and Ross reasoned that one means of putting the inhibition hypothesis to experimental test was offered by the apparent susceptibility of the electroencephalogram (EEG) to conditioning. If a photic stimulus, which tends to inhibit the alpha component of the EEG, is repeatedly paired with a neutral stimulus, such as a low-intensity tone, the neutral stimulus will tend to
WEISS B. Morrell and Ross's Central Inhibition in Cortical Conditioned Reflexes". AMA Arch NeurPsych. 1955;74(2):171-173. doi:10.1001/archneurpsyc.1955.02330140055010