Theta power reductions under cognitive load in amnestic mild cognitive impairment

Amnestic mild cognitive impairment (aMCI) is classified primarily via substantial episodic memory deficits in the absence of a dementia diagnosis. To investigate potential disruptions of memory-related brain function in this condition we compared QEEG power between 12 participants with aMCI and 12 matched healthy controls. EEG was acquired during performance of a modified Sternberg recognition task using study list lengths of 4 or 8 words (low and high memory load). While recognition accuracy of aMCI participants was lower than that of controls, this difference was not significant. Nevertheless the aMCI group demonstrated significantly lower theta power relative to the control group at frontal midline electrodes. Furthermore in the aMCI sample only, theta power was significantly lower under high versus low memory load. Given that theta oscillations are proposed to reflect not purely memory function but also more general processes such as cognitive control, the current data indicate that amnestic deficits in aMCI may reflect more generalised cognitive deficits. Moreover these outcomes provide novel neurophysiological evidence that such deficits are exacerbated under higher cognitive load. If replicated in larger samples such findings would have substantial implications for current concepts of amnestic MCI