Brain plasticity and stroke recovery
Year: 2012
Type: dissertation
Study design: Observational Study
Abstract: Brain plasticity and stroke recovery Recovery from stroke is based on the capability of the brain to reorganize its structure and function after lesion. An acute stroke triggers a cascade of time-dependent metabolic and physiological reactions, which enable changes in the organization and function of widespread cortical regions. A wide range of studies, using various functional imaging methods, have thrown light on the reorganizational changes after stroke. However, less is known about the temporal evolution of these changes and their correlation to clinical recovery. In this thesis, different aspects of neurophysiological changes related to sensorimotor recovery were studied in 18 patients with first-ever stroke in the middle cerebral artery territory, affecting upper limb motor function. Follow-up recordings of somatosensory evoked fields (SEF) and spontaneous rhythmic brain activity were performed with whole-head MEG within 1 week (T0), 1 month (T1), and 3 months (T2) after stroke with concomitant evaluation of clinical outcome. MEG suits stroke studies especially well, as it is independent from hemodynamic alterations, and the signals are practically unaffected by morbid tissue. The results indicated that the hand representation in the primary somatosensory cortex (SI) in the affected hemisphere (AH) was transiently enlarged at T1 and returned to normal size concomitantly with clinical improvement of hand function (Study I). Study II showed that the activation in the contralateral secondary somatosensory cortex (cSII) was decreased in the AH at T0 and increased during follow-up. The strength of cSII activation paralleled the recovery of hand function during the 3 months follow-up, suggesting that cSII may be an important region in mediating the somatosensory input to the motor cortex. The results in Study III indicated that afferent-input-modulated motor cortex excitability was increased in the AH in the acute phase after stroke and decreased during follow-up in association with recovery of hand function. Study IV showed that the ~10-Hz oscillations were enhanced in the AH at T1 and T2. Moreover, pathological perilesional low-frequency oscillations were detected in 7/16 patients at T0, and the low-frequency oscillations persisted for at least 3 months in 4 patients. These 4 patients had a worse clinical outcome at T2 than the rest of the patients. The results indicate that even small lesions can cause widespread neurophysiological changes in the cortical network. Certain brain regions, such as SII, seem to be specifically important for the recovery of hand function. The results underline the importance of parallel recovery of the somatosensory and motor systems for fluent hand function. The most evident neurophysiological changes were observed within 1 month after stroke in parallel with steepest improvement of clinical recovery, suggesting that the first 4 weeks are critical for functional recovery.
Source: Työväentutkimus Vuosikirja
Author: Kristina Laaksonen
Language: English
Subfield: Rehabilitation
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2150855947