Intensity and inter‐stimulus‐interval effects on human middle‐ and long‐latency auditory evoked potentials in an unpredictable auditory context

Abstract

It is not known how Auditory‐Evoked Responses (AERs) comprising Middle Latency Responses (MLRs) and Long Latency Responses (LLRs) are modulated by stimulus intensity and inter‐stimulus interval (ISI) in an unpredictable auditory context. Further, intensity and ISI effects on MLR and LLR have never been assessed simultaneously in the same humans. To address this important question, thirty participants passively listened to a random sequence of auditory clicks of three possible intensities (65, 75, and 85 dB) at five possible ISI ranges (0.25 to 0.5 s, 0.5 to 1 s, 1 to 2 s, 2 to 4 s, 4 to 8 s) over four to seven one‐hour sessions while EEG was recorded. P0, Na, Pa, Nb, and Pb MLR peaks and N1 and P2 LLR peaks were measured. MLRs P0 (p = .005), Pa (p = .021), and Pb (p = <.001) were modulated by intensity, while only MLR Pb (p = <.001) was modulated by ISI. LLR N1 and P2 were modulated by both intensity and ISI (all p values < .001). Intensity and ISI interacted at Pb, N1, and P2 (all p values < .001), with greater intensity effects at longer ISIs and greater ISI effects at louder intensities. Together, these results provide a comprehensive picture of intensity and ISI effects on AER across the entire thalamocortical auditory pathway, while controlling for stimulus predictability. Moreover, they highlight P0 as the earliest MLR response sensitive to stimulus intensity and Pb (~50 ms) as the earliest cortical response coding for ISIs above 250 ms and showing an interdependence between intensity and ISI effects.

Omission responses in local field potentials in rat auditory cortex

“…For the 3 Hz rate, such general adaptation effects may be arguably stronger than for the “edge” rates of 2 Hz and 4H z, possibly resulting in attenuated response amplitudes, and weaker effects attributable to previous stimuli within the 3 Hz sequences. Another possibility is that our effects may be due to a non-monotonic effect of presentation rate on evoked response amplitudes, as it has been shown in humans that auditory evoked N1 amplitudes first decrease as a function of increasing presentation rate (up to ~ 3 Hz), and then increase for even faster rates [ 44 ]. Nevertheless, the gradual buildup of omission signals over time observed for the remaining rates is consistent with the literature on mismatch responses following repetition suppression to consecutive standards [ 45 , 46 ], as well as with a recent study showing a gradual buildup of predictive information (decodable from auditory cortex in anaesthetised rats) as a function of the number of preceding predictable stimuli [ 47 ].…”