LONG-TERM MODIFICATIONS OF SYNAPTIC EFFICACY IN THE HUMAN INFERIOR AND MIDDLE TEMPORAL CORTEX

The primate temporal cortex has been demonstrated to play an important role in visual memory and pattern recognition, It is of particular in terest to investigate whether activity-dependent modification of synap tic efficacy, a presumptive mechanism for Learning and memory, is pres ent in this cortical region. Here we address this issue by examining t he induction of synaptic plasticity in surgically resected human infer ior and middle temporal cortex. The results show that synaptic strengt h in the human temporal cortex could undergo bidirectional modificatio ns, depending on the pattern of conditioning stimulation. High frequen cy stimulation (100 or 40 Hz) in layer IV induced long-term potentiati on (LTP) of both intracellular excitatory postsynaptic potentials and evoked field potentials in layers II/III. The LTP induced by 100 Hz te tanus was blocked by 50-100 mu M DL-2-amino-5-phosphonovaleric acid, s uggesting that N-methyl-D-aspartate receptors were responsible for its induction, Long-term depression (LTD) was elicited by prolonged low f requency stimulation (1 Hz, 15 min), It was reduced, but not completel y blocked, by DL-2-amino-5-phosphonovaleric acid, implying that some o ther mechanisms in addition to N-methyl-D-aspartate receptors were inv olved in LTD induction. LTD was input-specific, i.e., low frequency st imulation of one pathway produced LTD of synaptic transmission in that pathway only. Finally, the LTP and LTD could reverse each other, sugg esting that they can act cooperatively to modify the functional state of cortical network, These results suggest that LTP and LTD are possib le mechanisms for the visual memory and pattern recognition functions performed in the human temporal cortex.