Effect of attention on neural tuning

Attention refers to our amazing ability to focus on the relevant bits of information amongst the vast inflow of sensory information. Here, we studied the effect of attention in the human auditory cortex using both electroencephalography (EEG) and magnetoencephalography (MEG). We specifically hypothesized that attention sharpens the tuning of neural responses, as opposed to a simple increase in gain. A psychophysical experiment using auditory stimuli was conducted, measuring simultaneously either EEG or MEG. In the experiment, sine tones of 1000 Hz were presented with a continuous noise masker. The masker was generated by bandstop filtering white noise with a varying notch width (±500...0) around 1000 Hz. The notch width was kept constant during the acquisition of each event-related potential and event-related field. The experiment included three different conditions: two attended conditions where subject was instructed to pay attention either to frequency or duration difference, and one passive condition where the subject watched a silent movie, with the auditory stimuli in the background. The results suggest that attention modulates the amplitudes of the neural responses. Amplitudes of the auditory evoked potential components (P50, N100 and P200) were modulated so that especially the N100 amplitude was significantly higher in the attended conditions than in the passive condition. However, this happened only when the notch widths were relatively small, suggesting that the effect was not only gain-based, causing an overall stronger neural activation, but also involved sharpening of sound frequency tuning of the auditory cortex neurons. This information can be adapted to clinical attention deficiency studies or diagnoses, where e.g. Alzheimer's disease, schizophrenia or ADHD-syndrome patients are involved. By using a suitable set of auditory stimuli and comparing the neural responses linked to stimulus to ones from healthy people, an indicative measure of the gravity of attention deficiency could be obtained.