Age-related changes in MEG theta and alpha oscillatory signatures of attentional control

In our recent behavioural research (Callaghan et al., 2017), we reported age-related changes in the costs of switching between from a temporal (rapid serial visual presentation) to a spatial (visual search) attention task. Using magnetoencephalography, we have now compared the neural signatures of attention refocusing between three age groups (19-30, 40-49 and 60+ years) and found differences in task-related modulation and cortical localisation of alpha and theta oscillations. Efficient, faster switching between the temporal and spatial attention tasks in the youngest group compared to both older groups was reflected in parietal theta effects that were significantly reduced in the older groups. Residual parietal theta activity in older individuals was, however, beneficial to attentional switching, and could reflect the preservation of attention mechanisms. Difficulties in refocusing attention in the older and middle-aged adults (slowed response times) were accompanied by reduced theta power modulation in occipital and cerebellar regions. In addition to this posterior theta deficit, older and middle-aged adults presented with increased recruitment of frontal (both groups) and temporal (older group) areas. Theta oscillations therefore demonstrated a posterior to anterior processing shift, which may reflect the engagement of alternative strategies in older- and middle-age, such as top-down attentional control in an attempt to compensate for posterior processing deficits. Additional frontal theta recruitment indeed appeared to be beneficial for faster performance, as reflected by correlational analysis. Temporal theta (in older-age), however, did not correlate with performance, but could reflect strategies unrelated to speeded performance (e.g. silent vocalisation to maintain task goals). Alpha oscillations did not significantly correlate with task performance, possibly reflecting decreased neural precision or de-differentiation, but require further investigation.