The effects of attentional load on auditory ERPs recorded from human cortex

Responses to acoustic input were recorded from human temporal cortex using subdural electrodes in order to investigate in greater anatomical detail how attentional load modulates exogenous auditory responses. Four patient-volunteers performed a dichotic listening task in which they listened for rare frequency deviants in a series of tones presented to both ears at interstimulus intervals (ISIs) of 400, 800, and 2000 ms. Across all ISIs, stimuli presented contralateral to electrode location produced the strongest deflections in the averaged ERP at approximately 90 and 170 ms post-stimulus on average (labeled N90stg and P170stg). Maximal recording sites for these peaks most often occurred over the Sylvian fissure or the upper bank of the posterior superior temporal gyrus. Neither ISI nor selective attention exhibited substantial effects on peak latencies. However, as presentation rates increased (decreasing ISI), overall averaged event-related potential (ERP) amplitudes declined significantly, while attending to the contralateral stimulus significantly increased both the N90stg and P170stg peaks for most patients. This effect of attention increased with decreasing ISI for both components most clearly in the difference between the grand-average ERPs for attending to vs. ignoring the contralateral stimulus, and even more dramatically in the percentage ratio of that difference over the mean peak amplitude. This amplifying effect of attention with increasing load, along with its anatomical location, suggests that attention can enhance exogenous sources in auditory cortex.