Abstract
The pharmacological treatment of Alzheimer’s disease (AD) is often limited and accompanied by drug side effects. Thus alternative therapeutic strategies such as non-invasive brain stimulation are needed. Few studies have demonstrated that transcranial direct current stimulation (tDCS), a method of neuromodulation with consecutive robust excitability changes within the stimulated cortex area, is beneficial in AD. There is also evidence that tDCS enhances memory function in cognitive rehabilitation in depressive patients, Parkinson’s disease, and stroke. tDCS improves working and visual recognition memory in humans and object-recognition learning in the elderly. AD’s neurobiological mechanisms comprise changes in neuronal activity and the cerebral blood flow (CBF) caused by altered microvasculature, synaptic dysregulation from ß-amyloid peptide accumulation, altered neuromodulation via degenerated modulatory amine transmitter systems, altered brain oscillations, and changes in network connectivity. tDCS alters (i) neuronal activity and (ii) human CBF, (iii) has synaptic and non-synaptic after-effects (iv), can modify neurotransmitters polarity-dependently, (v) and alter oscillatory brain activity and (vi) functional connectivity patterns in the brain. It thus is reasonable to use tDCS as a therapeutic instrument in AD as it improves cognitive function in manner based on a disease mechanism. Moreover, it could prove valuable in other types of dementia. Future large-scale clinical and mechanism-oriented studies may enable us to identify its therapeutic validity in other types of demential disorders.
Highlights
As the pharmacological treatment in Alzheimer disease (AD) is limited (Bauer, 2006), alternative therapeutic approaches are worth pursuing, such as non-invasive brain stimulation with transcranial direct current.Transcranial direct current stimulation is the application of weak electrical currents by saline-soaked surface sponge electrodes to different cortical areas. transcranial direct current stimulation (tDCS) can polaritydependently modulate cortical excitability with prolonged aftereffects (Nitsche et al, 2005) and modify neuronal excitability by tonic de-or hyperpolarization of the resting membrane potential (Creutzfeld et al, 1962; Purpura and McMurtry, 1965)
TDCS has demonstrated efficacy in improving recognition memory in Alzheimer’s disease (AD) (Boggio et al, 2009, 2011) and it is a useful tool in cognitive neurorehabilitation, as improvements in cognitive functions were described in patients with depression (Fregni et al, 2006), Parkinson’s disease (Boggio et al, 2006) and stroke (Monti et al, 2008)
We describe tDCS application in clinical studies in patients with dementia and studies on cognitive functions as well as potential underlying mechanisms in this article
Summary
Reviewed by: Luiz Kobuti Ferreira, Universidade de Sao Paulo, Brazil Pedro Shiozawa, Santa Casa de Misericórdia de São Paulo, Brazil. There is evidence that tDCS enhances memory function in cognitive rehabilitation in depressive patients, Parkinson’s disease, and stroke. TDCS alters (i) neuronal activity and (ii) human CBF, (iii) has synaptic and non-synaptic after-effects (iv), can modify neurotransmitters polarity-dependently, (v) and alter oscillatory brain activity and (vi) functional connectivity patterns in the brain. It is reasonable to use tDCS as a therapeutic instrument in AD as it improves cognitive function in manner based on a disease mechanism. It could prove valuable in other types of dementia.
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