Preserved Transcallosal Inhibition to Transcranial Magnetic Stimulation in Nondemented Elderly Patients with Leukoaraiosis

Abstract

Structural corpus callosum (CC) changes in patients with leukoaraiosis (LA) are significantly associated with cognitive and motor impairment. The aim of this study is to investigate the transcallosal fibers functioning by means of transcranial magnetic stimulation (TMS) in elderly patients with LA. The resting motor threshold (rMT), the motor-evoked potentials (MEPs), and the controlateral (cSP) and ipsilateral silent periods (iSP) were determined using single-pulse TMS in 15 patients and 15 age-matched controls. The neuropsychological profile and the vascular burden at brain magnetic resonance imaging (MRI) were concomitantly explored. Patients reported abnormal scores at tests evaluating executive control functions. No significant difference was found in TMS measures of intra- and intercortical excitability. No CC lesion was evident at MRI. Transcallosal inhibitory mechanisms to TMS seem to be spared in LA patients, a finding which is in line with neuroimaging features and suggests a functional integrity of the CC despite the ischemic interruption of corticosubcortical loops implicated in cognition and behavior. The observed neurophysiological finding differs from that reported in degenerative dementia, even in the preclinical or early stage. In our group of patients, the pure extent of LA is more related to impairment of frontal lobe abilities rather than functional callosal changes.

Cortical Plasticity in Depression

“…These symptoms may even present in the preclinical or early stages of these diseases (Bella et al., 2011a, 2011b, 2013; Lanza et al., 2013; Pennisi et al., 2016; Lanza et al., 2017). …”

Update on the Neurobiology of Vascular Cognitive Impairment: From Lab to Clinic

“…Therefore, a total of 46 papers were eventually included in this study ( Figure 1) and the main findings are summarized in Table 1. More in details, 8 studies deal with serum biomarkers [9][10][11][12][13][14][15][16], 10 with cerebrospinal fluid (CSF) [17][18][19][20][21][22][23][24][25][26], 4 with neuroimaging [27][28][29][30], 6 with histopathology [31][32][33][34][35][36], and 14 with transcranial magnetic stimulation (TMS) [37][38][39][40][41][42][43][44][45][46][47][48][49][50]; 4 studies included more than one technique: one studied both serum and CSF markers [51], two both serum and neuroimaging [52,53], and one both CSF and neuroimaging…”

“…A two-year follow-up study in the same patients showed an increase of the global cortical excitability (reduction of the median rMT), along with a significant cognitive worsening [41], thus suggesting the role of the enhanced ICF at baseline as a predictor of cognitive and TMS progression. Finally, unlike MCI and AD, TMS measures of transcallosal functioning appeared to be spared in mild VCI, suggesting a role of the interhemispheric integrity in holding cognitive performance up in these patients [42].…”

“…Among neurophysiological techniques, TMS is a non-invasive tool evaluating cortical excitability, synaptic plasticity, and functional connectivity in vivo and in "real time", in physiological conditions [70][71][72] and in a number of psychiatric and neurological disorders [73][74][75][76][77][78], including cognitive impairment and dementia [42,49,79], also providing neurochemical insights [80][81][82][83].…”

Current Pathogenetic Concepts of Vascular Cognitive Impairment

“…a) Post-ischemic encephalopathy with several types of predominant distribution pattern: (1) Recent neurophysiological studies using transcranial motor stimulation (TMS) have revealed distinct patterns of cortical excitability in VaD, possibly associated with disease process and progress [43,44]. However, the pathophysiological details of VCI/VaD and of vascular depression (VaDep -see consensus paper [45]) are beyond the scope of this mini-review.…”