Sang Seok Yeo

Functional Role of the Corticoreticular Pathway in Chronic Stroke Patients

Background and Purpose— The corticoreticular pathway (CRP) is known to be an important extrapyramidal tract for walking ability. However, little is known about the functional role of the CRP in recovery of walking ability. We investigated relation between the CRP and walking ability in chronic hemiparetic stroke patients. Methods— Among 209 consecutive patients, 54 patients, who showed complete injury of the corticospinal tract (CST) in the affected hemisphere on diffusion tensor tractography, and 20 normal subjects were recruited. Functional ambulation category was used in measurement of walking ability. The fractional anisotropy value, apparent diffusion coefficient value, and fiber volume of the CRP and CST were used for the diffusion tensor imaging parameters. Results— In the affected hemisphere, no significant difference in diffusion tensor imaging parameters of the CRP was observed between patient subgroups. In the unaffected hemisphere, patients who were able to walk showed significantly increased fiber volume of the CRP, compared with patients who could not walk and normal control subjects (P<0.05), without significant difference in fractional anisotropy and apparent diffusion coefficient values. In addition, the fiber volume of the CRP in the unaffected hemisphere showed positive correlation with functional ambulation category (P<0.05). In contrast, diffusion tensor imaging parameters of the CST in the unaffected hemisphere showed no correlation with functional ambulation category (P>0.05). Conclusions— The increased fiber volume of the CRP in the unaffected hemisphere seems to be related to walking ability in patients with chronic stroke. Therefore, the compensation of the CRP in the unaffected hemisphere seems to be one of the mechanisms for recovery of walking ability after stroke.

Corticoreticular pathway in the human brain: diffusion tensor tractography study.

The corticoreticular pathway (CRP) is involved in postural control and locomotor function. No study has been conducted for identification of the CRP in the human brain. In the current study, we attempted to identify the CRP in the human brain, using diffusion tensor tractography (DTT). We recruited 24 healthy volunteers for this study. Diffusion tensor images were scanned using 1.5-T. For reconstruction of the CRP, a seed region of interest (ROI) was placed on the reticular formation of the medulla. The first target ROI was placed on the midbrain tegmentum and the second target ROI was placed on the premotor cortex (Brodmann area 6). Values of fractional anisotropy, mean diffusivity, and tract volume of the CRP were measured. The CRP, which originated from the premotor cortex, descended through the corona radiata and the posterior limb of the internal capsule anterior to the corticospinal tract. In the midbrain and pons, it passed through the tegmentum and terminated at the pontomedullary reticular formation. No differences in terms of fractional anisotropy, mean diffusivity, and tract volume were observed between hemispheres (P>0.05). We identified the CRP in the human brain using DTT. These methods and results would be helpful to both clinicians and researchers in the neuroscience field.

Corticospinal Tract Change in the Unaffected Hemisphere at the Early Stage of Intracerebral Hemorrhage: A Diffusion Tensor Tractography Study

Objectives: Contribution by the unaffected hemisphere is one of the motor recovery mechanisms following stroke. We attempted to investigate changes in the corticospinal tract (CST) in the unaffected hemisphere at the early stage in patients with intracerebral hemorrhage (ICH), using diffusion tensor tractography (DTT). Subjects and Methods: Fifty-three consecutive hemiparetic patients and 40 age- and sex-matched control subjects were enrolled. DTT was performed using a 1.5-tesla system at the early stage of ICH (7–28 days after onset). We measured the fiber number, fractional anisotropy and apparent diffusion coefficient of CST tractography in the unaffected hemisphere, and assessed the motor function of the affected extremities. Results: The fiber number of the CST in the unaffected hemisphere of the patient group was higher than that of the control group (p = 0.000). In contrast, the fractional anisotropy value was lower than that of the control group (p = 0.018). However, there were no significant differences in the apparent diffusion coefficient values between the 2 groups (p = 0.654). Conclusions: We demonstrated that the CST in the unaffected hemisphere was changed at the early stage in patients with ICH, using DTT.

Evidence of Corticospinal Tract Injury at Midbrain in Patients With Subarachnoid Hemorrhage

Background and Purpose— Clear elucidation of the exact pathophysiological mechanisms of motor weakness in patients with subarachnoid hemorrhage has not yet been achieved. We attempted to investigate injury to the corticospinal tract in patients with subarachnoid hemorrhage using diffusion tensor imaging. Methods— Twenty-two patients with subarachnoid hemorrhage and 24 control subjects were recruited for this study. DTI-Studio software was used for reconstruction of the corticospinal tract. We measured fractional anisotropy and apparent diffusion coefficient values at 5 regions of interest along the corticospinal tract pathway including: the corona radiata, the posterior limb of the internal capsule, the upper midbrain, the midpons, and the upper medulla. Results— Fractional anisotropy value for the midbrain region of interest was lower in the patient group compared with the control group without change of apparent diffusion coefficient value (P<0.05). By contrast, fractional anisotropy and apparent diffusion coefficient values of the other 4 regions of interest were not different between the patient and control groups. Conclusions— Injury of the corticospinal tract at the midbrain was observed in patients with subarachnoid hemorrhage. Injury of the corticospinal tract at the midbrain appears to be one of the various pathophysiological mechanisms for motor weakness after subarachnoid hemorrhage.

Neural reorganization following bilateral injury of the fornix crus in a patient with traumatic brain injury.

OBJECTIVE We report on a patient who appeared to demonstrate neural reorganization after head trauma resulting in bilateral injury of the fornix crus. CASE REPORT A 58-year-old male patient and 8 control subjects were recruited. The patient had undergone head trauma as the result of a car accident and had lost consciousness for 30 min. Brain magnetic resonance imaging, performed 3 years after the head trauma, showed no evidence of abnormality. RESULTS Discontinuation of both crus in the proximal region was observed on diffusion tensor tractography of the fornix. In the right fornix, an abnormal neural tract originating from the right crus passed through the splenium of the corpus callosum to connect with the right inferior longitudinal fasciculus. By contrast, in the left fornix, another abnormal neural tract originating from the left column passed through the left inferior longitudinal fasciculus and the splenium of the corpus callosum. None of these abnormal neural tracts was observed in normal subjects. CONCLUSION We presume that the abnormal neural tracts of the fornix observed in this patient were the result of neural reorganization triggered by bilateral injury of the fornix crus. The results of this study suggest a mechanism for recovery of the injured fornix following head trauma.

The cortical activation pattern by a rehabilitation robotic hand: a functional NIRS study

Introduction: Clarification of the relationship between external stimuli and brain response has been an important topic in neuroscience and brain rehabilitation. In the current study, using functional near infrared spectroscopy (fNIRS), we attempted to investigate cortical activation patterns generated during execution of a rehabilitation robotic hand. Methods: Ten normal subjects were recruited for this study. Passive movements of the right fingers were performed using a rehabilitation robotic hand at a frequency of 0.5 Hz. We measured values of oxy-hemoglobin (HbO), deoxy-hemoglobin (HbR) and total-hemoglobin (HbT) in five regions of interest: the primary sensory-motor cortex (SM1), hand somatotopy of the contralateral SM1, supplementary motor area (SMA), premotor cortex (PMC), and prefrontal cortex (PFC). Results: HbO and HbT values indicated significant activation in the left SM1, left SMA, left PMC, and left PFC during execution of the rehabilitation robotic hand (uncorrected, p < 0.01). By contrast, HbR value indicated significant activation only in the hand somatotopic area of the left SM1 (uncorrected, p < 0.01). Conclusions: Our results appear to indicate that execution of the rehabilitation robotic hand could induce cortical activation.

Precommissural fornix in the human brain: a diffusion tensor tractography study.

Purpose Other than a single case report, no diffusion tensor tractography (DTT) studies of the precommissural fornix in the human brain have been conducted. In the current study, we attempted to visualize the precommissural fornix in the human brain using DTT. Materials and Methods We recruited 36 healthy volunteers for this study. Diffusion tensor images were scanned using a 1.5-T scanner, and the precommissural fornix was analyzed using Functional Magnetic Resonance Imaging of the Brain (FMRIB) software. Values of fractional anisotropy (FA), mean diffusivity (MD), and tract volume of the precommissural fornix were measured. Results The precommissural fornix originated from the hippocampal formation on each hemisphere as a crus; both crura were then joined to the body of the fornix. The body of the fornix continued anteriorly to the level just superior to the anterior commissure, where it divided into each column of the precommissural fornix. Each column descended anteriorly to the anterior commissure and terminated in the septal nuclei. Values of FA, MD, and tract volumes of the precommissural fornix did not differ between the right and left hemispheres (p>0.05). Conclusion We believe that the methodology and results of this study would be helpful to future research on the precommissural fornix and in the elucidation of the pathology of diseases involving the precommissural fornix.

Thalamocortical connections between the mediodorsal nucleus of the thalamus and prefrontal cortex in the human brain: a diffusion tensor tractographic study.

Purpose The elucidation of thalamocortical connections between the mediodorsal nucleus (MD) of thalamus and the prefrontal cortex (PFC) is important in the clinical fields of neurorehabilitation and psychiatry. However, little is known about these connections in human brain. We attempted to identify and investigate the anatomical characteristics of the thalamocortical connection between MD and PFC in human brain using diffusion tensor tractography (DTT). Materials and Methods Thirty-two healthy volunteers were recruited for this study. Diffusion tensor images were scanned using a 1.5-T. A seed region of interest was placed at the MD of the thalamus on coronal images, and target regions of interest were placed on the dorsolateral prefrontal cortex (DLPFC), the ventrolateral prefrontal cortex (VLPFC), and the orbitofrontal cortex (OFC), respectively. The three thalamocortical connections found were reconstructed using Functional Magnetic Resonance Imaging of the Brain (FMRIB) software. Results The three thalamocortical connections were arranged in subcortical white matter in the following order from upper to lower levels: the DLPFC, the VLPFC, and the OFC. In terms of fractional anisotropy and mean diffusivity values, no significant differences were observed between the DLPFC, VLPFC and OFC (p>0.05). In contrast, the OFC tract volume was higher than those of the DLPFC and the VLPFC (p<0.05). Conclusion Three thalamocortical connections were reconstructed between MD and PFCs in human brain using DTT. We believe that the results of this study would be helpful to clinicians in treating frontal network syndrome and psychiatric diseases.

Contribution of the pedunculopontine nucleus on walking in stroke patients.

Objectives: We attempted to investigate changes of the pedunculopontine nucleus (PPN) according to walking ability in chronic stroke patients, using diffusion tensor imaging (DTI). Methods: 55 consecutive chronic stroke patients who were not able to walk due to injury of the corticospinal tract (CST) at stroke onset and 22 age-matched normal control subjects were recruited. We measured the values of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) of the PPN and assessed the walking ability of each patient. Results: In patients who were able to walk independently, the FA value of the PPN in the affected hemisphere was increased without change of the ADC value (p < 0.05). Increase of the FA value was positively correlated with the degree of walking ability (p < 0.05). In contrast, the ADC value was increased in the affected hemisphere of patients who could not walk, without change of the FA value (p < 0.05). This increase of the ADC value was negatively correlated with the degree of walking ability (p < 0.05). Conclusion: We found that the neuronal activity of the PPN in the affected hemisphere was increased in stroke patients who were able to walk independently. Therefore, we think that the PPN in the affected hemisphere contributed to walking ability in stroke patients with CST injury.

Transpontine Connection Fibers between Corticospinal Tracts in Hemiparetic Patients with Intracerebral Hemorrhage

Objectives: A connection of fibers between corticospinal tracts (CSTs) at the pons, originating from the CST of the affected hemisphere, has been observed in hemiparetic patients with stroke. The authors investigated the incidence and the clinical significance of transpontine connection of fibers (TCFs) in hemiparetic patients with intracerebral hemorrhage (ICH), using diffusion tensor tractography (DTT). Subjects and Methods: Forty-two patients with ICH with weakness of the affected extremities at the time of DTI scanning and 41 age-matched control subjects were recruited. TCFs were classified into three types according to severity: type A – no TCF extending to the opposite hemisphere, type B – a TCF crossing to the opposite hemisphere and ending at the subcortical level, and type C – a TCF crossing the pons and ascending to the cortex of the opposite hemisphere. Results: TCFs originating from the CST in affected and unaffected hemispheres were significantly more prevalent among patients than controls (both p < 0.05). In addition, TCF severity was found to be closely related to motor function reduction in affected extremities (p < 0.05) and to extent of CST injury in affected hemispheres (p < 0.05). Conclusions: TCF appears to represent a compensatory mechanism associated with motor weakness or CST injury in patients with ICH.