Synaptic de?ciency in Alzheimer disease and its implications on thalamic and cortical oscillations: a study using a neural mass model

This paper studies the effects of varying the totalnumber of synapses in a computational model of a thalamocortico-thalamic circuitry. The aim is to study overall EEGslowing in Alzheimer disease (AD) indicated by an increase inpower within the delta (0.5-3 Hz) and theta (3.5-7 Hz) bandsand a decrease in power within the alpha (7.5-13 Hz) and beta(13.5-20 Hz) frequency bands. We observe a systematic shiftin peak power of the model output from the highest (beta) tothe lowest (delta) frequency band with intra-thalamic synapticdepletion. This conforms to an overall EEG slowing observedin AD. Furthermore, the power in all bands stabilise beyonda certain threshold and do not change with further increasein synaptic connectivity. This implies redundancy in synapticpathways of the thalamo-cortical circuitry and conforms to thetheory of cognitive reserve in AD.