The study of the neuronal organization of the hedgehog associative cortical zone revealed that besides primitive characteristics this area possesses a number of progressive features. An electrophysiological approach revealed a great number of polysensory neurons. The method, based on the HRP retrograde axonal transport, enabled us to discover the connections between primitive associative LP and MD thalamic nuclei and the associative cortex. Motor conditioned reflexes connected with visual discrimination as well as reflexes to signals of different modalities were elaborated quite easily. Conditioning to a simultaneous visual-auditory complex was found impossible in hedgehogs. Bilateral ablation of associative area results in disruption of the fine components of sensorimotor integration. It is likely that a primitively organized associative system in hedgehogs participates in the formation of sensorimotor synthesis, but fails to realize complex acts of intersensory integration.

Unit activity in the frontal cortex (s. principalis) during the performance of a complex behavior program--nonspecific expectation after a warning stimulus, conditioned stimulus, and delay period, trigger signal, and alternative choice, followed by food award--was studied by the multineuronal recording method. Processes of combination of external stimuli into an integrated program, retention of stimulus traces in the memory, and correct and incorrect problem solving were reflected in the unit activity of s. principalis. The level of the correct responses of choice and the corresponding correlates in modifications of unit activity depended directly on the level of food motivation. The results are discussed from the standpoint of the evolutionary formation of the thalamo-frontal association system of the brain, connected with the formation of behavior programs in accordance with current biological motivation.

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