Abstract
Starting from the early 2000s, paired associative stimulation (PAS) protocols have been used in humans to study brain connectivity in motor and sensory networks by exploiting the intrinsic properties of timing-dependent cortical plasticity. In the last 10 years, PAS have also been developed to investigate the plastic properties of complex cerebral systems, such as the frontal ones, with promising results. In the present work, we review the most recent advances of this technique, focusing on protocols targeting frontal cortices to investigate connectivity and its plastic properties, subtending high-order cognitive functions like memory, decision-making, attentional, or emotional processing. Overall, current evidence reveals that PAS can be effectively used to assess, enhance or depress physiological connectivity within frontal networks in a timing-dependent way, in turn modulating cognitive processing in healthy and pathological conditions.
Highlights
Paired associative stimulation (PAS) is a protocol of non-invasive brain stimulation in which a sensory, peripheral stimulus is repeatedly paired with a transcranial magnetic stimulation (TMS) pulse over a cortical area known to be activated by the former stimulus
By varying the inter-stimulus interval (ISI) between these stimulations, PAS protocols can affect synaptic plasticity, inducing long-term potentiation (LTP)-like and depression (LTD)-like after-effects on cortical excitability [i.e., Spike-timing-dependent plasticity (STDP); e.g., Caporale and Dan, 2008] in the stimulated cortical area or circuit (e.g., Stefan et al, 2000; Wolters et al, 2003)
In 2013, the PAS protocol was used for the first time to induce STDP in frontal areas by targeting the dorsolateral prefrontal cortex
Summary
Starting from the early 2000s, paired associative stimulation (PAS) protocols have been used in humans to study brain connectivity in motor and sensory networks by exploiting the intrinsic properties of timing-dependent cortical plasticity. In the last 10 years, PAS have been developed to investigate the plastic properties of complex cerebral systems, such as the frontal ones, with promising results. We review the most recent advances of this technique, focusing on protocols targeting frontal cortices to investigate connectivity and its plastic properties, subtending high-order cognitive functions like memory, decision-making, attentional, or emotional processing. Current evidence reveals that PAS can be effectively used to assess, enhance or depress physiological connectivity within frontal networks in a timing-dependent way, in turn modulating cognitive processing in healthy and pathological conditions
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