Activation of the mirror neuron system in treatment of aphasia

Introduction: Based on assumptions about the so called mirror neuron system, this study evaluates a new kind of naming therapy for aphasic patients. It is hypothesized that both, perception and execution of object-related movements should facilitate object naming in aphasia. In addition to behavioural assessment, fMRI is conducted pre and post treatment. It is well known that there are 'mirror neurons' in the macaque frontal cortex that fire during both action production and action perception. A similar multimodal integration effect has been demonstrated for the human brain. Motor and premotor activation was present when subjects watched object-related hand movements [1]. Furthermore there is evidence for a functional link between language associated cortex prefrontal areas and the hand motor area in the dominant hemisphere [2]. In a recent study, excitability of the left hand-area was enhanced during language tasks even though no hand motor response was required [3]. These findings led to the assumption that spoken language may have developed from a gestural language and therefore still is strictly linked to hand motor areas. It is the goal of the present study to find further evidence for the hypothesis of a strong connection between language- and hand-related areas of inferior frontal cortex, and to clarify the so far unresolved issue to what extend the mirror neuron system is operative for language in either hemisphere. Depending on site of lesion in aphasia, the mirror-neuron system might be still operative in the lesioned dominant hemisphere or might become the basis of functional language compensation in the nondominant right hemisphere.[4].

Subjects: Treatment was applied to seven right handed aphasic patients (5 male, 2 female; age ranging from 38 to 65 years) with severe naming disorder as diagnosed by the Aachen Aphasia Test. All patients suffered from a single vascular stroke. Duration of aphasia varied between 7 to 30 months post stroke.

Methods: We applied a special naming treatment in which manipulable objects were presented to the patients in four different conditions: 1) as static photos, 2) within short videos including a related hand movement, 3) within short videos including a non-related hand movement, 4) as static photos with the instruction to produce a related right hand gesture prior to naming. Each condition consisted of twelve items which had to be repeated four times each session with decreasing cues in order to provide errorless learning. The patients were trained twice a day over a period of twelve days. Overall, each condition was trained in six different sessions in a systematically varied order. Following the mirror neuron assumption, we expected conditions 2 and 4 to result in significantly better naming performance than conditions 1 and 3. In addition to behavioural data we acquired imaging data with the help of fMRI. Patients had to carry out the four training conditions in a 3Tesla scanner. Here we expected that conditions 2 and 4 should lead to a similar activation pattern involving premotor cortex areas whereas conditions 1 and 3 should not enhance the mirror neuron system.

Results: As expected better naming performance was achieved in condition 2. In contrast, condition 4 did not result in the expected facilitation effect which we attribute to presence of right sided hemiparesis in all patients examined so far. First inspection of fMRI images shows a right hemisphere activation of the mirror neuron system in conditions 2. and 4.

References:

[1] Iacoboni M, Woods RP, Brass M, Bekkering H, Mazziotta JC, Rizzolatti G (1999): Cortical mechanisms of human imitation. Science 286:2526–28;

[2] Tokimura H, Tokimura Y, Oliviero A, Asakura T, Rothwell JC (1996): Speech-induced changes in corticospinal excitability. Annals of Neurology 40:628–34;

[3] Meister IG, Boroojerdi B, Foltys H, Sparing R, Huber W, Töpper R (2003): Motor cortex hand area and speech: implications fort the development of language. Neuropsychologia 41:401–06;

[4] Grande M, Huber W (2006): Aphasie, in: Fink G, Schneider F (eds.) Funktionelle MRT in Psychiatrie und Neurologie, Springer, Berlin