Lesion location may attenuate response to strategy training in acute stroke

Dopaminergic mesolimbic structural reserve is positively linked to better outcome after severe stroke

The concept of brain reserve capacity has emerged in stroke recovery research in recent years. Imaging-based biomarkers of brain health have helped to better understand outcome variability in clinical cohorts. Still, outcome inferences are far from being satisfactory, particularly in patients with severe initial deficits. Neurorehabilitation after stroke is a complex process, comprising adaption and learning processes, which, on their part, are critically influenced by motivational and reward-related cognitive processes. Amongst others, dopaminergic neurotransmission is a key contributor to these mechanisms. The question arises, whether the amount of structural reserve capacity in the dopaminergic system might inform about outcome variability after severe stroke. For this purpose, this study analysed imaging and clinical data of 42 severely impaired acute stroke patients. Brain volumetry was performed within the first 2 weeks after the event using the Computational Anatomy Toolbox CAT12, grey matter volume estimates were collected for seven key areas of the human dopaminergic system along the mesocortical, mesolimbic and nigrostriatal pathways. Ordinal logistic regression models related regional volumes to the functional outcome, operationalized by the modified Rankin Scale, obtained 3-6 months after stroke. Models were adjusted for age, lesion volume and initial impairment. The main finding was that larger volumes of the amygdala and the nucleus accumbens at baseline were positively associated with a more favourable outcome. These data suggest a link between the structural state of mesolimbic key areas contributing to motor learning, motivational and reward-related brain networks and potentially the success of neurorehabilitation. They might also provide novel evidence to reconsider dopaminergic interventions particularly in severely impaired stroke patients to enhance recovery after stroke.

Therapies Targeting Stroke Recovery

Stroke recovery therapeutics include many classes of intervention and numerous treatment targets. Stroke is a very heterogeneous disease. As such, stroke recovery therapeutics benefit from a personalized medicine approach that considers intersubject differences, such as in infarct location or stroke severity, when assigning treatment. Prediction of treatment responders can be improved by incorporating biological measures, such as neural injury and neural function, as the bedside behavioral phenotype has an incomplete relationship with the biological events underlying stroke recovery. Another ramification of high variability between patients is the need to examine effects of restorative therapies in relation to dose, time poststroke, and stroke severity in clinical trials. For example, enrollment across a wide time interval poststroke or in a population with a very broad range of deficits means high variance across patients in the biological state of the brain. The doses of rehabilitation therapy being studied are often low; it takes substantial practice to acquire a skill in the healthy brain; this is more, not less, pronounced after a stroke. Recognition and treatment of poststroke depression represents a major unmet need. These points are considered in the context of a review of recent advances in stroke recovery therapeutics.