Journal
JOURNAL OF NEUROSCIENCE
Volume 28, Issue 42, Pages 10631-10640Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.3333-08.2008
Keywords
inferior temporal cortex; prefrontal cortex; repetition suppression; macaques; size selectivity; fMRI adaptation
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Funding
- Geconcerteerde Onderzoeksacties K.U. Leuven [GOA/2005/18]
- Excellentiefinanciering K. U. Leuven [EF/05/014]
- Interuniversitaire Attractiepool Belgium [IUAP P6/29]
- Geneeskundige Stichting Koningin Elisabeth
- Human Frontier Science Program
- Fund for Scientific Research (FWO) Flanders
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Repetition of a stimulus results in decreased responses in many cortical areas. This so-called adaptation or repetition suppression has been used in several human functional magnetic resonance imaging studies to deduce the stimulus selectivity of neuronal populations. We tested in macaque monkeys whether the degree of neural adaptation depends on the similarity between the adapter and test stimulus. To manipulate similarity, we varied stimulus size. We recorded the responses of single neurons to different-sized shapes in inferior temporal (IT) and prefrontal cortical (PFC) areas while the animals were engaged in a size or shape discrimination task. The degree of response adaptation in IT decreased with increasing size differences between the adapter and the test stimuli in both tasks, but the dependence of adaptation on the degree of similarity between the adapter and test stimuli was limited mainly to the earlyphase of the neural response in IT. PFC neurons showed only weak size-contingent repetition effects, despite strong size selectivity observed with the same stimuli. Thus, based on the repetition effects in PFC, one would have erroneously concluded that PFC shows weak or no size selectivity in such tasks. These findings are relevant for the interpretation of functional magnetic resonance adaptation data: they support the conjecture that the degree of adaptation scales with the similarity between adapter and test stimuli. However, they also show that the temporal evolution of adaptation during the course of the response, and differences in the way individual regions react to stimulus repetition, may complicate the inference of neuronal tuning from functional magnetic resonance adaptation.
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