Anatomo-Functional Origins of the Cortical Silent Period: Spotlight on the Basal Ganglia

Abstract

The so-called cortical silent period (CSP) refers to the temporary interruption of electromyographic signal from a muscle following a motor-evoked potential (MEP) triggered by transcranial magnetic stimulation (TMS) over the primary motor cortex (M1). The neurophysiological origins of the CSP are debated. Previous evidence suggests that both spinal and cortical mechanisms may account for the duration of the CSP. However, contextual factors such as cortical fatigue, experimental procedures, attentional load, as well as neuropathology can also influence the CSP duration. The present paper summarizes the most relevant evidence on the mechanisms underlying the duration of the CSP, with a particular focus on the central role of the basal ganglia in the “direct” (excitatory), “indirect” (inhibitory), and “hyperdirect” cortico-subcortical pathways to manage cortical motor inhibition. We propose new methods of interpretation of the CSP related, at least partially, to the inhibitory hyperdirect and indirect pathways in the basal ganglia. This view may help to explain the respective shortening and lengthening of the CSP in various neurological disorders. Shedding light on the complexity of the CSP’s origins, the present review aims at constituting a reference for future work in fundamental research, technological development, and clinical settings.

Neuro-Behavioral Correlates of Executive Dysfunctions in Dyslexia Over Development From Childhood to Adulthood

“…Interestingly, also subcortical regions were found to show hypoactivation during a phonological processing task in children with dyslexia, such as the basal ganglia ( Kita et al, 2013 ), in addition to the left extrastriate cortex ( Backes et al, 2002 ) and the right cerebellum ( van Ermingen-Marbach et al, 2013 ). Considering the importance of mutual exchanges between cortical and subcortical regions ( Zeugin and Ionta, 2021 ), these findings demonstrate how more basic learning mechanisms related to cortico-subcortical-cerebellar activations are also different in children with dyslexia. It has been proposed that this hyperactivation in the above-mentioned EF regions and hypoactivation of visual processing and language-related regions is related to the pathology of dyslexia, through a greater attempt of recognizing words holistically and retrieving the semantic meaning of it from working memory and allocating greater attention for error detection to compensate for hypoactivation in visual and reading-related areas.…”

The flubbed body: Pathological body size representation in personal neglect

“…Recent studies have postulated that PN should be considered as a disconnection syndrome in which white matter tracks that underly body representation are damaged, rather than discrete modular lesions (Bertagnoli et al, 2022;Committeri et al, 2007; see also Committeri et al, 2018 for a revision). It is also possible that basal ganglia, known to change their role depending on the pathway involved in a specific function (Zeugin and Ionta, 2021), work differently in patients with PN who present with an impaired body representation network. Further anatomical studies can help shed light on this aspect.…”

Inter-Individual Variability in Motor Output Is Driven by Recruitment Gain in the Corticospinal Tract Rather Than Motor Threshold

“…This is because MEP amplitude is the most widely recorded outcome measure in TMS studies for which we have a large amount of data from multicentric studies [ 31 , 32 ]. However, recent studies have revealed the importance of cortical silent period as a neurophysiological index to assess the status of cortical and spinal motor neurons [ 47 ]. Considering other such parameters may further enhance our understanding of the neural underpinnings of inter-individual variability.…”