DEVELOPMENT OF INFERIOR TEMPORAL CORTEX IN THE MONKEY

Inferior temporal (IT) cortex is critical for visual pattern recogniti on in adult primates. However, the functional development of IT cortex appears to be incomplete until late in the first year of life in monk eys and probably beyond. Responses of neurons in IT are substantially weaker, of longer latency, and more susceptible to anesthesia within a t least the first half year of life. In addition, refinement of connec tions of IT, particularly those with regions in the opposite hemispher e and with regions related to memory and attention, continues for at l east several months after birth. Moreover, many of the pattern recogni tion functions that IT supports in adulthood themselves show a very pr otracted period of development, and damage to IT cortex in infancy app ears to have relatively little effect on pattern recognition abilities , despite the pronounced effects of comparable damage in adulthood. Th ese findings all suggest that IT undergoes an extended period of postn atal development, during which both visual experience and the maturati on of other brain structures may contribute to the emergence of mechan isms of pattern recognition within IT. In other respects, fundamental characteristics of IT emerge quite early. For example, despite their w eaker responses, IT neurons have adult-like patterns of responsiveness -including pronounced form selectivity and large bilateral receptive f ields-as early as we were able to test (similar to 6 weeks). Thus, IT cortex appears to be prewired with (or predisposed to develop rapidly) neural circuitry sufficient to produce basic properties remarkably si milar to those found in the adult animal. Future studies of IT cortex will need to address the development of signals related to perceptual constancies and to formation and retrieval of visual object memories, the development of interactions with other regions involved in visual recognition (particularly frontal cortex), and the specific mechanisms underlying various types of plasticity present in IT cortex in both d eveloping and mature primates.