Endogenous auditory spatial attention modulates obligatory sensory activity in auditory cortex

Endogenous attention is the self-directed focus of attention to a region or feature of the environment. In this study, we assess the effects of endogenous attention on temporally detailed responses to continuous and competing auditory stimuli obtained using the novel auditory evoked spread spectrum analysis (AESPA) method. There is some debate as to whether an enhancement of sensory processing is involved in endogenous attention. It has been suggested that attentional effects are not due to increased sensory activity but are due to engagement of separate temporally overlapping nonsensory attention-related activity. There are also issues with the fact that the influence of exogenous attention grabbing mechanisms may hamper studies of endogenous attention. Due to the nature of the AESPA method, the obtained responses represent activity directly related to the stimulus envelope and thus predominantly correspond to obligatory sensory processing. In addition, the continuous nature of the stimuli minimizes exogenous attentional influence. We found attentional modulations at ~136 ms (during the Nc component of the AESPA response) and localized this to auditory cortex. Although the involvement of separate nonsensory attentional centers cannot be ruled out, these findings clearly demonstrate that endogenous attention does modulate obligatory sensory activity in auditory cortex.