Selective Attention Modulates Activity in the Auditory Nerve
Post by Lina Teichmann
The takeaway
Studying the effects of selective attention on subcortical structures is usually not feasible in humans, however, testing cochlear implant (CI) users offers a unique opportunity to examine how top-down effects modulate activity in the auditory nerve. Using a cross-modal attention task, the current study shows that activity in the auditory nerve in humans is modulated by attention.
What's the science?
Attention relies on selecting relevant features from our environment while ignoring irrelevant features. For example, when listening to someone speak, we are able to focus our attention on the words they are saying while ignoring irrelevant background sounds. Direct evidence from animal studies suggests that these attentional mechanisms modulate auditory nerve action potentials. Studying similar effects in humans is usually difficult, as direct recordings from the auditory nerve are generally not feasible. However, this week in the Journal of Neuroscience, Gehmacher, Reisinger and colleagues present data from CI users, showing that auditory nerve activity in humans is modulated by attention.
How did they do it?
A group of CI users completed a cross-modal attention task while recordings were taken from a coil that temporarily replaced their CI. In every trial, participants saw a cue on a computer screen (either an eye or ear) to indicate whether to attend to an auditory or visual stimulus. Then an audiovisual stimulus was presented. The auditory stimulus was a tone delivered directly to the CI coil. The visual stimulus was a circle with black and white stripes oriented vertically. In some trials, oddball auditory (slightly different tone) and visual (slightly tilted version of visual stimulus) stimuli were presented, and participants were asked to press a button when they detected an oddball in the cued domain.
What did they find?
Using a frequency analysis, the results showed that cochlear activity was modulated by selective attention. In the theta frequency range (5-8Hz), a higher power was associated with attending to the auditory domain. Relating these results to a concurrently recorded electroencephalography (EEG) dataset from one participant, the authors showed that the auditory nerve, as opposed to a source located elsewhere in the brain, was the most likely origin of the signal. Lastly, the authors showed that classification algorithms trained on single-trial activity recorded from the CI could distinguish whether the participant was attending to the visual or auditory stimulus. Together, these results support the hypothesis that auditory nerve activity is modulated by attention in humans.
What's the impact?
Previous work has shown that the neural signal is modulated by attention at the cortical level. However, evidence for attentional modulation in subcortical structures such as the cochlea was scarce, partially because direct recordings in humans are usually not feasible. The current study addressed this gap in the literature by studying auditory nerve activity directly in CI users. The results highlight that auditory nerve activity is modulated by attention in humans, providing new insights into the interplay between top-down and bottom-up effects in hearing.