Abstract
Stimulus-specific adaptation (SSA) in single neurons of the auditory cortex was suggested to be a potential neural correlate of the mismatch negativity (MMN), a widely studied component of the auditory event-related potentials (ERP) that is elicited by changes in the auditory environment. However, several aspects on this SSA/MMN relation remain unresolved. SSA occurs in the primary auditory cortex (A1), but detailed studies on SSA beyond A1 are lacking. To study the topographic organization of SSA, we mapped the whole rat auditory cortex with multiunit activity recordings, using an oddball paradigm. We demonstrate that SSA occurs outside A1 and differs between primary and nonprimary cortical fields. In particular, SSA is much stronger and develops faster in the nonprimary than in the primary fields, paralleling the organization of subcortical SSA. Importantly, strong SSA is present in the nonprimary auditory cortex within the latency range of the MMN in the rat and correlates with an MMN-like difference wave in the simultaneously recorded local field potentials (LFP). We present new and strong evidence linking SSA at the cellular level to the MMN, a central tool in cognitive and clinical neuroscience.
Highlights
A critical function of the brain is to identify uncommon and potentially important stimuli while ignoring irrelevant ambient backgrounds [1,2,3]
Stimulus-specific adaptation (SSA) is present in primary auditory cortex (A1) and the other two primary fields, it is markedly stronger in the nonprimary fields posterior auditory field (PAF) and suprarhinal auditory field (SRAF), consistent with the SSA observed in nonlemniscal parts of the inferior colliculus (IC) and medial geniculate body (MGB)
To study the topographic distribution of SSA across the auditory cortex, we recorded a total of 816 multiunit activity (MUA) clusters from layers IIIb/IV within all cortical fields from the left auditory cortex in 12 animals
Summary
A critical function of the brain is to identify uncommon and potentially important stimuli while ignoring irrelevant ambient backgrounds [1,2,3] In humans, this ability is reflected by an electrophysiological brain response called mismatch negativity (MMN), a mid-late (150–200 ms) deflection of the auditory event-related potentials (ERP) that is elicited by uncommon, but not by repetitive, sounds [4,5,6,7] and serves to automatically redirect attention toward potentially relevant stimuli [8]. Previous studies on the general response properties of the auditory cortex reported that nonprimary neurons in the cat [20,21] and rat [22,23,24] auditory cortex adapt more strongly than in A1. Two recent studies that mapped auditory ERPs in the rat showed robust MMN-like responses in nonprimary auditory cortical fields [28,29]
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