Development of inferior temporal cortex in the monkey.

Inferior temporal (IT) cortex is critical for visual pattern recognition in adult primates. However, the functional development of IT cortex appears to be incomplete until late in the first year of life in monkeys and probably beyond. Responses of neurons in IT are substantially weaker, of longer latency, and more susceptible to anesthesia within at least the first half year of life. In addition, refinement of connections of IT, particularly those with regions in the opposite hemisphere and with regions related to memory and attention, continues for at least several months after birth. Moreover, many of the pattern recognition functions that IT supports in adulthood themselves show a very protracted period of development, and damage to IT cortex in infancy appears to have relatively little effect on pattern recognition abilities, despite the pronounced effects of comparable damage in adulthood. These findings all suggest that IT undergoes an extended period of postnatal development, during which both visual experience and the maturation of other brain structures may contribute to the emergence of mechanisms of pattern recognition within IT. In other respects, fundamental characteristics of IT emerge quite early. For example, despite their weaker responses, IT neurons have adult-like patterns of responsiveness--including pronounced form selectivity and large bilateral receptive fields--as early as we were able to test (approximately 6 weeks). Thus, IT cortex appears to be prewired with (or predisposed to develop rapidly) neural circuitry sufficient to produce basic properties remarkably similar 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 developing and mature primates.