Masaharu Maruishi

Compensatory cortical activation during performance of an attention task by patients with diffuse axonal injury: a functional magnetic resonance imaging study

Objective: To determine how cortical compensation occurs in higher cognitive systems during the recovery phase of diffuse axonal injury (DAI). Design: 12 right-handed patients with a magnetic resonance imaging (MRI) lesion pattern compatible with pure DAI were identified. Pure DAI was defined as finding of traumatic microbleeds on T2*-weighted gradient-echo images in the absence of otherwise traumatic or non-traumatic MRI abnormalities. 12 matched healthy controls were also enrolled. Functional magnetic resonance imaging (fMRI) was used to assess brain activation during a working memory test (Paced Visual Serial Attention Test (PVSAT)). Results: No significant group differences were observed in reaction times for the PVSAT. Although patients with pure DAI committed a few errors during the PVSAT, controls respond correctly to each probe. Controls showed activations in the left frontal gyrus, left parietal gyrus and right inferior parietal gyrus. Patients with pure DAI showed activations in the left inferior frontal gyrus, right inferior frontal gyrus and right middle frontal gyrus. Between-group analysis of the PVSAT task showed significantly greater activation of the right inferior frontal gyrus (BA 45) and right middle frontal gyrus (BA 9) in patient with pure DAI versus controls. Conclusions: Patients with pure DAI require compensatory activation of the contralateral (right) prefrontal region to carry out activities similar to healthy controls. These findings provide further evidence for the adaptive capacity of neuronal systems and brain plasticity during the recovery stages of DAI.

The pathophysiology of prospective memory failure after diffuse axonal injury - Lesion-symptom analysis using diffusion tensor imaging

BackgroundProspective memory (PM) is one of the most important cognitive domains in everyday life. The neuronal basis of PM has been examined by a large number of neuroimaging and neuropsychological studies, and it has been suggested that several cerebral domains contribute to PM. For these activation studies, a constellation of experimental PM trials was developed and adopted to healthy subjects. In the present study, we used a widely used clinical PM assessment battery to determine the lesions attributable to PM failure, with the hypothesis that lesion-symptom analysis using diffusion tensor imaging (DTI) in subjects with diffuse axonal injury (DAI) can reveal the neuronal basis of PM in everyday life.ResultsFourteen DAI patients (age: range of 18-36, median 24) participated in this study. PM failure was scored in the range of 0-6 using three sub-tests of the Rivermead Behavioural Memory Test. The PM scores of DAI patients were in the range of 2-6 (median 4.5, inter-quartile range 2.25). The severity of axonal injury following DAI was examined using fractional anisotropy (FA), one of the DTI parameters, at voxel level in each subject. We then obtained clusters correlated with PM failure by conducting voxel-based regression analysis between FA values and PM scores. Three clusters exhibited significant positive correlation with PM score, the left parahippocampal gyrus, left inferior parietal lobe, and left anterior cingulate.ConclusionsThis is the first lesion-symptom study to reveal the neuronal basis of PM using DTI on subjects with DAI. Our findings suggest that the neuronal basis of PM is in the left parahippocampal gyrus, left inferior parietal lobe, and/or left anterior cingulate. These findings are similar to those of previous activation studies with loading experimental PM tasks.

Brain activations in errorless and errorful learning in patients with diffuse axonal injury: A functional MRI study

Primary objective: Errorless learning has been reported to be effective in the rehabilitation of patients with impaired cognitive functions following brain injury. This study compared brain activations in errorless learning (EL) and errorful learning (EF) in patients with diffuse axonal injury (DAI) using a functional magnetic resonance imaging (fMRI). Methods and procedures: The participants were 13 patients with DAI. Thirteen healthy individuals were evaluated as a control group. The participants learned words under the EL and EF conditions in advance and performed the recognition task during fMRI scanning. Main outcomes and results: EL in the control group was significantly faster than EF (p = 0.005), but not in the DAI group. EL in the DAI group scored significantly higher than EF (p = 0.026). An fMRI showed significant activations in the posterior cingulate gyrus (BA 31) and precuneus (BA 7) in the control group when EF > EL, but in the precuneus (BA 7, 31) and bilateral inferior parietal lobules (BA 39, 40) in the DAI group. Conclusions: These results indicate the disadvantage of EF and advantage of EL to DAI patients. The findings also reflect brain plasticity in patients with DAI in the chronic phase.

A virtual prosthetic hand using EMG signals for fMRI measurements

This paper proposes a virtual EMG-prosthetic hand system using a neural network available in an fMRI room. A subject attaches surface electrodes on his forearm, and manipulates the virtual EMG-prosthetic hand visualized with 3D computer graphics by using visual biofeedback projected on a screen in the scan room. The preliminary experiments demonstrate that the intended hand motion by the subject can be determined with high discrimination rates over 96% without decaying fMRI images. Finally, in order to show the validity of the proposed system, we report the neurological experiments that were carried out to analyze human brain functions.

Rehabilitation technique facilitates association cortices in hemiparetic patients: functional MRI study

We used fMRI to study brain activation with facilitative rehabilitation techniques (passive hand movements and visual feedback) in two patients with subcortical lesions. Two tasks were given in a sequence. The first task (trial 1) was repetitive hand grasping by the paretic hand at a rate of 0.5 Hz with the eyes closed. The second task (trial 2), the facilitative rehabilitation technique, included task 1 plus support by a trainer to move the paretic hand with the eyes open to get visual feedback of the movement. The data were analyzed by a subtractive method. When task 1 was subtracted from task 2, it was found that the bilateral visual cortex, contralateral premotor cortex and posterior parietal cortex were involved with the passive hand movement and visual feedback. These facilitative rehabilitation techniques may integrate networks between sensory information and motor commands, and lead to functional reorganization.

GRAND ROUNDS: Familiarity Effect on Retrieval: A Neuropsychological Case Study

NM, who suffered traumatic brain injury (TBI) to the prefrontal cortex (PFC), was compared with a diffuse axonal injury (DAI) patient on tasks of free recall, cued recall and recognition memory. We manipulated the familiarity of items to explore the effects of item strength on retrieval. On free recall, NM performed best during the high-familiarity picture condition. On cued recall, he performed best during the high-familiarity word condition. Although high familiarity improved his accuracy on picture items in free recall, low familiarity improved his recognition of words. The patient with DAI did not show these patterns. The role of the PFC in memory is discussed in terms of plausible recognition processes.