Sensorimotor cortex excitability and connectivity in Alzheimer's disease: A TMS-EEG Co-registration study

Abstract

Several studies have shown that, in spite of the fact that motor symptoms manifest late in the course of Alzheimer's disease (AD), neuropathological progression in the motor cortex parallels that in other brain areas generally considered more specific targets of the neurodegenerative process. It has been suggested that motor cortex excitability is enhanced in AD from the early stages, and that this is related to disease's severity and progression. To investigate the neurophysiological hallmarks of motor cortex functionality in early AD we combined transcranial magnetic stimulation (TMS) with electroencephalography (EEG). We demonstrated that in mild AD the sensorimotor system is hyperexcitable, despite the lack of clinically evident motor manifestations. This phenomenon causes a stronger response to stimulation in a specific time window, possibly due to locally acting reinforcing circuits, while network activity and connectivity is reduced. These changes could be interpreted as a compensatory mechanism allowing for the preservation of sensorimotor programming and execution over a long period of time, regardless of the disease's progression. Hum Brain Mapp 37:2083-2096, 2016. © 2016 Wiley Periodicals, Inc.

Predicting individual brain functional connectivity using a Bayesian hierarchical model

“…Compared to the control group, both the MCI and AD disease groups demonstrated weaker positive connectivity within the auditory and sensorimotor networks and also weaker positive connections between these two networks. Some previous studies have found altered activity and connectivity in these two networks that are related to the Alzheimer disease (Agosta et al, 2010; Goll et al 2012; Salustri et al 2013; Terranova et al 2013; Ferreri et al 2016). …”

Motor Cortex Theta and Gamma Architecture in Young Adult APPswePS1dE9 Alzheimer Mice

“…Sensorimotor cortex excitability can be altered in Alzheimer patients [44, 45] and mouse models such as APPswePS1dE9 also exhibit motor impairments at late AD stage at 12 months of age [46]. The central question we addressed here is whether early cortical power alterations described in the frontal cortex of 16–17 wks old APPswePS1dE9 mice [30] are also present in cortical M1 deflections.…”

Emergence of neurophysiological biomarkers of Alzheimer disease

“…In particular, they can provide information on the function of specific cortical circuits of the AD brain, involving the cholinergic pathways and also the glutamatergic and GABAergic circuits5 and the level of brain plasticity (Motta et al ) 1. The combination of TMS with EEG can also evaluate cortico-cortical connectivity in AD 7. Moreover, TMS-related tests can assess the effects of drugs on the intact human brain.…”