Neuroimaging Advances in Stroke Rehabilitation Figure 2: Neural Correlates of Affected Hand-touch Discrimination in Contralesional Thalamus A B
0.8 1.0
0.2 0.6
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0 Contralesional thalamus 20406080 Tactile discrimination score
A: Axial slice depicting brain activation negatively correlated with tactile discrimination during stimulation of the affected hand in 19 stroke patients; B: Plot of relationship between the touch discrimination score (TDT) and task-related activation in stroke patients with subcortical lesions (rhombi) and cortical lesions (dots). In addition, activation data for 12 age-matched healthy controls (squares). Source: Carey et al., 2011.59
functionally altered due to transient ischemia and subsequent reperfusion. Both factors evoke a large number of biochemical, metabolic, and immunological processes that evolve sequentially.50
Notably, the binding of flumazenil, a γ-aminobutyric acid (GABA)A receptor antagonist, as measured with positron emission tomography, was found to be reduced in this area in proportion to the initial hypoperfusion as assessed with perfusion computed tomography.51
This
suggests loss of inhibitory interneurons in the peri-infarct area and consecutive increased cortical excitability, as demonstrated in TMS studies.52,53
The functionally abnormal perilesional tissue contributes to the clinical deficit, which will affect an activation-related signal: functional MRI (fMRI) performed approximately two days after stroke revealed an area in the ipsilesional postcentral gyrus and posterior cingulate that correlated with motor recovery approximately three months after stroke.54
Restoration of hand function three months
after stroke was associated with highly lateralized activation of the affected sensorimotor cortex which developed over time.55
Thus, when
an impaired function is probed in an activation study, the activation most likely reflects adaptation of the injured brain to the functional deficit owing to spontaneous recovery in the perilesional tissue. The perilesional cortex is anatomically linked to a large number of brain structures that become engaged as a functional network upon the generation of functional activity and in relation to spontaneous recovery. Since the first functional neuroimaging studies in neurological patients with focal brain lesions, it has been well established that there are large-scale changes affecting the contralesional cerebral cortex and subcortical structures in highly structured patterns, which most likely reflects the functional intracerebral connectivity. These functional changes are reminiscent of re-learning, as they represent activation patterns similar to procedural learning and are essentially transient in nature.52,53,56
The Role of the Somatosensory Cortex and the Thalamus
In daily life, intact somatosensation is crucial not only for perception, but also for guidance of action. Accordingly, tactile input, guidance of and activity in somatosensory brain regions have been linked to motor recovery post-stroke.57,58
US NEUROLOGY
The Effect of Rehabilitative Training and Underlying Neural Correlates
Rehabilitative training after stroke is known to improve the functionality and to enhance the spectrum of activities of daily living. Functional neuroimaging studies have provided evidence that training has a significant impact on the cerebral activation patterns: it has been shown that constraint-induced movement therapy, which focuses a patient’s attention to the affected side and involves repetitive training, resulted in improved motor function and enhanced activation in the partially damaged sensorimotor cortex66,67 structures including the hippocampus.68
as well as in other gray-matter Similarly, repetitive training of the
Furthermore, a three-week training in chronic stroke patients using robot-assisted training resulted in improvements of hand motor function which was associated with a greater fMRI signal in sensorimotor cortex related to performance of the movements trained by the robot.70
The severity of touch discrimination
affected arm yielded an increase of activation in the sensorimotor cortex related to hand movements, which initially persisted for weeks after training completion and then decreased in magnitude in relation to the functional gains.69
impairment experienced post-stroke correlated differentially with brain activity following lesions depending on lesion location in either subcortical or cortical somatosensory regions (see Figure 2). However, notably for subcortical lesions, touch outcome was inversely correlated with brain activity in widespread cortical and subcortical circuits during tactile stimulation of the affected hand.59
In contrast, in patients with
cortical lesions there was no correlation between touch discrimination and activation patterns.59
However, activity in the contralesional
It was argued that this would help to redress the imbalance in cortical activity between hemispheres that commonly occurs after stroke and is an important determinant of impairment and recovery.53,61 This could be influenced by interthalamic communication62
or via
feedback connections from cortical areas that play an important role in both rapid and more slowly emerging forms of thalamic plasticity.63–65
thalamus was inversely correlated with ipsilesional somatosensory cortex and positively correlated with the contralesional somatosensory cortex.60
Cluster: thalamus r=-0.78
This increase was task-specific, since it did not occur in relation to non-trained supination/pronation movements with the affected hand and movements of the non-trained hand. Similarly,
107
Activation (task – rest)
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