Suk Hoon Ohn

Time-dependent effect of transcranial direct current stimulation on the enhancement of working memory.

The time-dependent effect of transcranial direct current stimulation (tDCS) on working memory was investigated by applying anodal stimulation over the left prefrontal cortex. This single-blind, sham-controlled crossover study recruited 15 healthy participants. A three-back verbal working-memory task was performed before, during, and 30 min after 1 mA anodal or sham tDCS. Anodal tDCS, compared with sham stimulation, significantly improved working-memory performance. Accuracy of response was significantly increased after 20 min of tDCS application, and was further enhanced after 30 min of stimulation. This effect was maintained for 30 min after the completion of stimulation. These results suggest that tDCS at 1 mA enhances working memory in a time-dependent manner for at least 30 min in healthy participants.

Longitudinal Changes of Resting-State Functional Connectivity During Motor Recovery After Stroke

Background and Purpose— Functional MRI (fMRI) studies could provide crucial information on the neural mechanisms of motor recovery in patients with stroke. Resting-state fMRI is applicable to patients with stroke who are not capable of proper performance of the motor task. In this study, we explored neural correlates of motor recovery in patients with stroke by investigating longitudinal changes in resting-state functional connectivity of the ipsilesional primary motor cortex (M1). Methods— A longitudinal observational study using repeated fMRI experiments was conducted in 12 patients with stroke. Resting-state fMRI data were acquired 4 times over a period of 6 months. Patients participated in the first session of fMRI shortly after onset and thereafter in subsequent sessions at 1, 3, and 6 months after onset. Resting-state functional connectivity of the ipsilesional M1 was assessed and compared with that of healthy subjects. Results— Compared with healthy subjects, patients demonstrated higher functional connectivity with the ipsilesional frontal and parietal cortices, bilateral thalamus, and cerebellum. Instead, functional connectivity with the contralesional M1 and occipital cortex were decreased in patients with stroke. Functional connectivity between the ipsilesional and contralesional M1 showed the most asymmetry at 1 month after onset to the ipsilesional side. Functional connectivity of the ipsilesional M1 with the contralesional thalamus, supplementary motor area, and middle frontal gyrus at onset was positively correlated with motor recovery at 6 months after stroke. Conclusions— Resting-state fMRI elicited distinctive but comparable results with previous task-based fMRI, presenting complementary and practical values for use in the study of patients with stroke.

Enhancing motor performance by anodal transcranial direct current stimulation in subacute stroke patients.

Kim DY, Ohn SH, Yang EJ, Park C-I, Jung KJ: Enhancing Motor Performance by Anodal Transcranial Direct Current Stimulation in Subacute Stroke Patients. Objective:To investigate whether anodal transcranial direct current stimulation enhances motor performance in the paretic hand of subacute poststroke patients and how long the improvement persisted after the session. Design:Ten subacute poststroke patients who suffered stoke within 12 wks were recruited for this single-blinded, sham-controlled, crossover study. Anodal transcranial direct current stimulation or sham stimulation was randomly delivered on the hot spot of the first dorsal interosseous in the affected hemisphere. The duration of transcranial direct current stimulation was 20 mins and sham was 30 secs. The Box and Block test and finger acceleration measurement were performed before, during, immediately after, and 30 and 60 mins after anodal or sham stimulation to assess time-dependent changes in motor performance. Results:Finger acceleration measurement and Box and Block test were significantly improved after anodal transcranial direct current stimulation compared with sham stimulation (P < 0.05). Anodal transcranial direct current stimulation significantly improved Box and Block test for at least 60 mins and finger acceleration until 30 mins after stimulation (P < 0.05) without significant differences in attention and fatigue. Conclusions:Anodal transcranial direct current stimulation on the affected hemisphere can enhance motor performance of the hemiparetic hand transiently, outlasting the stimulation session.

Neural correlates of donepezil-induced cognitive improvement in patients with right hemisphere stroke: A pilot study

Donepezil has been proven effective in the treatment of Alzheimers disease and vascular dementia. However, its effects on the cognitive neural network have not been fully investigated. The purpose of this study was to evaluate the effect of donepezil on reorganisation of the cognitive neural network in patients with post-stroke cognitive impairment using functional MRI (fMRI). Fourteen patients with stroke in the right hemisphere were enrolled. Participants were randomly assigned to the experimental or the control group. Donepezil (5 mg) or placebo was administered daily for four weeks. Cognitive function assessment was performed before and immediately after treatment, and repeated one month after cessation of treatment. fMRI was performed before and after treatment. Ten out of 14 patients (six in the experimental group, four in the control group) successfully completed all experimental processes. The experimental group showed significant improvements in the Mini-Mental Status Examination during the post-treatment evaluation and one-month follow-up compared to the pre-treatment evaluation (p < .05). No improvement was observed in the control group. In the experimental group fMRI showed increased activation in both prefrontal areas, both inferior frontal lobes, and in the left inferior parietal lobe. Increased recruitment of the parieto-frontal networks in the selected patients was considered to be a neural correlate of cognitive improvement induced by donepezil.

Double decussated ipsilateral corticospinal tract in schizencephaly.

We report a patient with left hemiparesis because of schizencephaly affecting the right precentral gyrus and describe a double decussated ipsilateral corticospinal tract detected using the multimodal brain mapping technique. In this patient, we could observe that the unaffected primary motor cortex (M1) controls both hands by functional magnetic resonance imaging and motor-evoked potential study. We were also able to visualize the corticospinal tract originating from the unaffected M1 that passed through the internal capsule and cerebral peduncle on the same side. It then crossed over twice at the brain stem level to go down to the ipsilateral spinal cord. These findings show a unique pattern of brain reorganization in the recovery from early brain injury.

Novel Information on Anatomic Factors Causing Grasp Reflex in Frontal Lobe Infarction: A Case Report

We report a patient with a severe limitation of function in the right hand resulting from grasp reflex following a stroke affecting the left anterior cerebral artery region. We describe, using diffusion tensor tractography (DTT), a disconnection between the bilateral frontal lobes via the corpus callosum. The patient could not control his right hand at all, even though his bilateral corticospinal tracts were intact. We noted that over the infarcted lesion on DTT, the white matter was invisible from the corpus callosum to the prefrontal cortex. These findings reflected a unique pattern of white-matter disconnection between the ipsilateral medial frontal lobe and ipsilateral and contralateral frontal cortex causing hand function deterioration in the form of severe grasp reflex.

Hemispheric asymmetry of speed-dependent intercerebellar connectivity

The coordinated and timed movements of human limbs require interactive cerebellar functions. We investigated the function of intercerebellar connectivity in controlling the movement speed of both hands with functional MRI experiments. Nine healthy, right-handed subjects performed finger movements at lower and higher speeds, as instructed. With finger movements at a higher speed, regional responses in the bilateral cerebellum were increased in both hands. However, the contribution of the ipsilateral cerebellum to the contralateral cerebellum, which was assessed by psychophysiological interaction analysis, was increased only in the dominant hand. Results of this study indicated that there is a speed-dependent modulation of intercerebellar connectivity for finger movement and this modulation has hemispheric asymmetry.

Preliminary Investigation of Pain-Related Changes in Cerebral Blood Volume in Patients With Phantom Limb Pain

OBJECTIVE To investigate changes in the pain network associated with phantom limb pain, magnetic resonance imaging (MRI) was used to measure cerebral blood volume (CBV) in patients who had undergone unilateral arm amputation after electrical injury. DESIGN Case-controlled exploratory MRI study of CBV via MRI. SETTING University hospital. PARTICIPANTS Participants (N=26) comprised patients with phantom limb pain after unilateral arm amputation (n=10) and healthy, age-matched persons (n=16). INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES The intensity of phantom limb pain was measured using the visual analog scale (VAS). Depressive mood was assessed using the Hamilton Depression Rating Scale, and cognitive function was assessed using the Korean version of the Mini-Mental State Examination. Voxel-wise comparisons of relative CBV maps were made between amputees and controls over the entire brain volume. The relationship between individual participant CBV (measured in voxels) and VAS score was also examined. RESULTS Compared with control participants, amputees exhibited greater degrees of depression; significantly higher CBV in the bilateral medial frontal area (orbitofrontal cortex [OFC] and pregenual anterior cingulate cortex [pACC]); and significantly lower CBV in the right midcingulate cortex, posterior cingulate cortex, and primary somatosensory cortex. CBV increased in the contralateral and ipsilateral hemispheres of the amputated arm, regardless of the amputation side. This CBV increase in the OFC and pACC was strongly correlated with pain intensity in all amputees. CONCLUSIONS We observed increased CBV in regions associated with emotion in the cerebral pain network of patients who had undergone unilateral arm amputation after electrical injury. This study suggests that CBV changes were related to neuroplasticity associated with phantom limb pain.

Videofluoroscopy-Guided Balloon Dilatation for the Opening Dysfunction of Upper Esophageal Sphincter by Postoperative Vagus Nerve Injury: A Report on Two Cases

Dysphagia secondary to peripheral cranial nerve injury originates from weak and uncoordinated contraction-relaxation of cricopharyngeal muscle. We report on two patients who suffered vagus nerve injury during surgery and showed sudden dysphagia by opening dysfunction of upper esophageal sphincter (UES). Videofluoroscopy-guided balloon dilatation of UES was performed. We confirmed an early improvement of the opening dysfunctions of UES, although other neurologic symptoms persisted. While we did not have a proper comparison of cases, the videofluoroscopy-guided balloon dilatation of UES is thought to be helpful for the early recovery of dysphagia caused by postoperative vagus nerve injury.

Changes in Diffusion Metrics of the Red Nucleus in Chronic Stroke Patients With Severe Corticospinal Tract Injury: A Preliminary Study

Objective To explore plastic changes in the red nucleus (RN) of stroke patients with severe corticospinal tract (CST) injury as a compensatory mechanism for recovery of hand function. Methods The moderate group (MG) comprised 5 patients with synergistic hand grasp movement combined with limited extension, and the severe group (SG) included 5 patients with synergistic hand grasp movement alone. The control group (CG) included 5 healthy subjects. Motor assessment was measured by Motricity Index (MI). Diffusion tensor imaging was analyzed using fractional anisotropy (FA) and radial diffusivity (RD) in the individual regions of interest (ROIs)—bilateral internal capsule and anterior pons for CST injury and bilateral RN for rubrospinal tract (RST) injury. Results The SG showed a significantly lower MI score than the MG mainly due to differences in hand subscores. Significantly reduced FA was observed in both MG and SG compared with CG, while SG showed increased MD and RD in the affected ROIs of CST, and increased FA on the unaffected side compared with CG. However, in the RN ROI, a significantly increased FA and decreased RD on the unaffected side similar to the affected side were found only in the SG. The relative index of FA was lower and RD in SG was higher than in CG in RST. Conclusion The diffusion metrics of RST showed changes in patients with severe CST injury, suggesting that RST may play a role in the recovery of hand function in patients with severe CST injury.