Limited and inconsistent evidence exists regarding a difference in interhemispheric inhibition (IHI) between patients poststroke and individuals without a history of stroke, according to a study published in the Journal of Stroke and Cerebrovascular Diseases.
IHI is a key cortical mechanism for supporting motor control. Individuals with unilateral neurologic disorders can present with altered physiologic activity not only in the affected hemisphere, but in the unaffected hemisphere as well, the researchers explained. The objective of the current study was to explore whether bilateral brain changes are due to behavioral modifications caused by unilateral impairment or are reflective of functional changes in brain regions connected anatomically via transcallosal pathways.
A total of 5 databases were systematically examined to identify those studies that reported IHI measures in patients with unilateral neurologic conditions, such as stroke, amyotrophic lateral sclerosis, cerebral palsy, complex regional pain syndrome, and traumatic brain injury, and in healthy control individuals. All of the data derived from the analysis were grouped according to the measure used (ipsilateral silent period [ISP] and dual-coil), stimulated hemisphere, and stage of the condition (ie, subacute or chronic).
A total of 1372 unique studies were identified, with 14 of them included in this review. The 14 studies comprised 226 adults poststroke — 153 of whom were men — and 161 age-matched control individuals —82 of whom were men. The mean patient age ranged from 54 to 66 years among adults poststroke and from 49 to 64 years among healthy adults. Of the 14 studies, 13 were observational, and 1 was interventional. Overall, 8 of the 14 included studies investigated the chronic stage only, 2 studies evaluated the subacute stage only, 2 longitudinal studies analyzed patients from the subacute to the chronic stage, and 1 cross-sectional study investigated both the subacute and the chronic stage.
Further, 3 of the studies included in the review recruited individuals with either ischemic or hemorrhagic stroke, 7 included patients with ischemic stroke only, and 3 did not specify patients’ stroke pathology. Most of the studies included in the review had a small sample size and performed poorly with respect to the selection of a representative sample. About half of the studies did not indicate which criteria were used to identify the healthy control individuals.
The findings revealed that the ISP duration was longer among patients with stroke compared with control individuals (stimulation of dominant hemisphere), regardless of stroke stage. Additionally, motor-evoked potentials were less suppressed among individuals with subacute stroke (stimulation of the unaffected hemisphere) than in control individuals, which became reversed in those with chronic stroke.
The current study had several limitations. First, although the search strategy used was broad in nature, the only studies that satisfied inclusion criteria involved individuals with stroke, thus limiting the generalizability of the results. Further, only 4 studies included individuals with subacute stroke, whereas the remaining studies involved only patients with chronic stroke. Therefore, definitive conclusions could not be drawn regarding the impact of duration poststroke on IHI.
“Detection of altered interhemispheric inhibition appears to be dependent on the measure of interhemispheric inhibition and the stage of recovery,” the researchers noted. They concluded, “Rebalancing interhemispheric inhibition using neuromodulation is considered a promising line of treatment for stroke rehabilitation.”
Consistent alterations in IHI in adults with stroke were not demonstrated in the current study.
Disclosure: Some of the study authors have declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.
Gerges ANH, Hordacre B, Di Pietro F, Moseley GL, Berryman C. Do adults with stroke have altered interhemispheric inhibition? A systematic review with meta-analysis. J Stroke Cerebrovasc Dis. 2022;31(7):106494. doi:10.1016/j.jstrokecerebrovasdis.2022.106494