Résumé
The majority of stroke survivors do not use their paretic arm in daily life activities, and this is, in part, because they learned to not use their paretic arm before recovering. In seated reaching, the difference between spontaneous arm use (as in daily activities) and forced arm use of the paretic arm (when trunk movements are not allowed) provides the percentage of learned non- use of the paretic arm. Here, we sought for neural correlates of the learned non-use behaviour using fNIRS neuroimaging.
Two post-stroke individuals (52 years, ischemic middle cerebral artery), one right-handed with a right hemisphere lesion (4 m post-stroke; BB score: 61/1) and the other left handed with a left hemisphere lesion (6m post-stroke; BB score: 23/73) were required to perform a series of seated reaching movements with their paretic (P), non-paretic (NP), and both (BH) hand(s) using a blocked design (3 blocks, 20 s task and 20 s rest) in a free and then in a forced arm use (trunk restrained) condition allowing to compute the percentage of learned non-use.
For the subject with the left hemisphere lesion (right paretic arm) the learned non-use was 3.5% for P (0.3% for NP and 6.5% for BH). This patient had a large deficit in paretic arm function, which resulted in trunk movements both in the free-use and forced-use condition, and thus did not show a learned non-use effect.
For the subject with the right hemisphere lesion (left paretic arm), the learned non-use was 13% for P (30% for BH, 1% for NP). For this patient, we found differences in activation of the prefrontal cortex (PFC) and sensorimotor cortex (SMC) regions, between the free-use and forced-use conditions.
This pilot study has shown for the first time that fNIRS neuroimaging can be used in clinical settings to determine brain activation changes as a function of the learned non-use of the paretic arm after a stroke. However, further investigations are necessary to go beyond the present proof of concept.