Author:

Keywords:

adaptation, single unit activity, inferior temporal sulcus, Long adapter, repetition suppression

Abstract:

Repetition suppression, the attenuation of neural activity for repeated stimuli, is a well-known neural phenomenon in the macaque inferior temporal (IT) cortex and is also present in homologue occipito-temporal areas of the human brain. A previous adaptation study of primary visual cortex suggests that prolonged exposure to the adapter stimuli strengthens the adaptation effect in comparison to brief exposure of the same stimuli. Here we investigate whether this property of V1 neurons prevails in IT, an area hierarchically at a higher stage. To determine this we presented the adapter stimulus for 3 durations of 300, 1500 and 3000ms and the test stimulus for 300ms. The test stimuli followed the adapter stimulus with an interstimulus interval of 300ms. Single cell recordings were performed in the macaque lower bank of the superior temporal sulcus. Two stimuli (A, B) were selected from a set of 52 complex images of various object categories, based on their response strength. These stimuli were either presented in repetition trials, i.e. repetition of the same stimulus (AA, BB), or as in alternation trials, i.e. alternation of the stimuli (AB, BA). These trials were presented in a pseudorandom order. Our data show repetition suppression for both the short duration, 300ms, adapter (p < / 0.0001, 65 neurons) and the long duration, 3000ms, adapter (p< / 0.0001, 65 neurons). However, in contrast to primary visual cortical neurons, the degree of repetition suppression did not differ significantly on adapter duration (300 and 3000ms). This surprising data question simple activity-dependent fatigue models of repetition suppression.