The Role of White Matter Disconnection in the Symptoms Relating to the Anarchic Hand Syndrome: A Single Case Study

A preliminary study of white matter disconnections underlying deficits in praxis in left hemisphere stroke patients

Limb apraxia is a higher-order motor disorder often occurring post-stroke, which affects skilled actions. It is assessed through tasks involving gesture production or pantomime, recognition, meaningless gesture imitation, complex figure drawing, single and multi-object use. A two-system model for the organisation of actions hypothesizes distinct pathways mediating praxis deficits via conceptual, 'indirect', and perceptual 'direct' routes to action. Traditional lesion- symptom mapping techniques have failed to identify these distinct routes. We assessed 29 left hemisphere stroke patients to investigate white matter disconnections on deficits of praxis tasks from the Birmingham Cognitive Screening. White matter disconnection maps derived from patients' structural T1 lesions were created using a diffusion-weighted healthy participant dataset acquired from the human connectome project (HCP). Initial group-level regression analyses revealed significant disconnection between occipital lobes via the splenium of the corpus callosum and involvement of the inferior longitudinal fasciculus in meaningless gesture imitation deficits. There was a trend of left fornix disconnection in gesture production deficits. Further, voxel-wise Bayesian Crawford single-case analyses performed on two patients with the most severe meaningless gesture imitation and meaningful gesture production deficits, respectively, confirmed distinct posterior interhemispheric disconnection, for the former, and disconnections between temporal and frontal areas via the fornix, rostrum of the corpus callosum and anterior cingulum, for the latter. Our results suggest distinct pathways associated with perceptual and conceptual deficits akin to 'direct' and 'indirect' action routes, with some patients displaying both. Larger studies are needed to validate and elaborate on these findings, advancing our understanding of limb apraxia.

The effect of damage to the white matter network and premorbid intellectual ability on postoperative verbal short-term memory and functional outcome in patients with brain lesions

Cognitive reserve is the capacity to cope with cognitive decline due to brain damage caused by neurological diseases. Premorbid IQ has been investigated as a proxy for cognitive reserve. To date, no study has focused on the effects of premorbid IQ in patients with brain tumors, considering the damage to white matter tracts. We investigated whether a higher premorbid IQ has a beneficial impact on postoperative verbal short-term memory and functional outcomes in patients with brain tumors. A total of 65 patients with brain tumors (35 right and 30 left hemisphere lesions) and 65 healthy subjects participated in the study. We used multiple regression analysis to examine whether white matter tract damage and premorbid IQ affect postoperative verbal short-term memory, and the interaction effects of premorbid IQ with damage to white matter tract on postoperative verbal short-term memory. Path analysis was used to investigate the relationship between damage to the white matter tract and premorbid IQ on postoperative functional ability. Our results showed that damage to the left arcuate fasciculus affected postoperative functional ability through verbal short-term memory, working memory, and global cognition in patients with left hemisphere lesions. In the right hemisphere lesion group, high premorbid IQ had a positive effect on functional ability by mediating verbal short-term memory, verbal working memory, and global cognition. We found that damage to the eloquent pathway affected postoperative verbal short-term memory regardless of the premorbid IQ level. However, a higher premorbid IQ was associated with better postoperative verbal short-term memory and functional outcomes when the brain lesions were not located in a crucial pathway. Our findings suggest that premorbid IQ and damage to the white matter tracts should be considered predictors of postoperative functional outcomes.

The 'healthy side' of anosognosia for hemiplegia: Increased sense of agency for the unimpaired limb or motor compensation?

OBJECTIVES

Anosognosic patients show a lack of awareness for their hemiplegia coupled with a distorted sense of agency for the actions performed by the plegic limbs. Since anosognosia is often associated with right brain damage, this hemisphere seems to play a dominant role in monitoring awareness for motor actions. Therefore, we would expect that anosognosic patients show distorted awareness and sense of agency also for actions performed with the unimpaired limb.

METHOD

To test this hypothesis, we induced illusory actions that could be congruent or incongruent with a preceding verbal command. A group of 16 right brain-damaged patients performed this task and then rated i) their ability to anticipate the actions, ii) their sense of agency and iii) their sense of ownership for each limb. Measures of awareness, neglect and motor impairment were also considered for the patient group.

RESULTS

Following incongruent actions with the unimpaired limb, less aware patients showed a relatively mild distortion in all three aspects. In addition, we also found a crucial relationship between motor impairment (for the plegic limb) and sense of agency for both plegic and healthy limbs.

CONCLUSION

Although the distortion linked to both limbs supports the initial hypothesis that the right hemisphere is responsible for monitoring awareness for action for the whole body, our data also suggest that the observed distortion may be linked to a motor compensatory phenomenon, not necessarily related to awareness processes.

Motor awareness: a model based on neurological syndromes

Motor awareness is a complex, multifaceted construct involving the awareness of both (i) one's motor state while executing a movement or remaining still and (ii) one's motor abilities. The analysis of neurological syndromes associated with motor disorders suggests the existence of various different components which are, however, integrated into a model of motor awareness. These components are: (i) motor intention, namely, a conscious desire to perform an action; (ii) motor monitoring and error recognition, that is, the capacity to check the execution of the action and identify motor errors; and (iii) a general awareness of one's own motor abilities and deficits, that is, the capacity to recognize the general state of one's motor abilities about the performance of specific actions and the potential consequences of motor impairment. Neuroanatomical correlates involving the parietal and insular cortices, the medial and lateral frontal regions, and subcortical structures (basal ganglia and limbic system) support this multi-component model. Specific damage (or disconnections) to these structures results in a number of different disorders in motor awareness, such as anosognosia for hemiplegia and apraxia, and a number of symptoms which are specific to motor intention disorders (e.g., the Anarchic Hand Syndrome and Tourette's Syndrome) or motor monitoring (e.g., Parkinson's and Huntington's diseases). All of these clinical conditions are discussed in the light of a motor awareness model.

Could Brain-Computer Interface Be a New Therapeutic Approach for Body Integrity Dysphoria?

Patients suffering from body integrity dysphoria (BID) desire to become disabled, arising from a mismatch between the desired body and the physical body. We focus here on the most common variant, characterized by the desire for amputation of a healthy limb. In most reported cases, amputation of the rejected limb entirely alleviates the distress of the condition and engenders substantial improvement in quality of life. Since BID can lead to life-long suffering, it is essential to identify an effective form of treatment that causes the least amount of alteration to the person's anatomical structure and functionality. Treatment methods involving medications, psychotherapy, and vestibular stimulation have proven largely ineffective. In this hypothesis article, we briefly discuss the characteristics, etiology, and current treatment options available for BID before highlighting the need for new, theory driven approaches. Drawing on recent findings relating to functional and structural brain correlates of BID, we introduce the idea of brain-computer interface (BCI)/neurofeedback approaches to target altered patterns of brain activity, promote re-ownership of the limb, and/or attenuate stress and negativity associated with the altered body representation.