Local morphology informs location of activation during navigation within the parahippocampal region of the human brain.

The relationship between the local morphological features that define the entorhinal and parahippocampal cortex in the medial temporal region of the human brain and activation as measured during a navigation task with functional magnetic resonance imaging was examined individually in healthy participants. Two functional activation clusters were identified one within the caudal end of the collateral sulcus proper and the other in the parahippocampal extension of the collateral sulcus, clearly establishing the activation in the posterior parahippocampal cortex. A third activation cluster was identified where the anterior segment of the collateral sulcus proper gives way to the posterior segment, demonstrating also activation within the middle parahippocampal cortex. No activation was observed in the entorhinal cortex that lies medial to the rhinal sulcus or in the anterior part of the parahippocampal cortex along the anterior branch of the collateral sulcus proper. The activations could also be clearly differentiated from the cortex of the fusiform and lingual gyri that lie laterally and posteriorly. These findings demonstrated specific activation in the middle and posterior part of the parahippocampal cortex when information necessary for navigation was retrieved from a previously established cognitive map and demonstrate that the sulci that comprise the collateral sulcal complex represent important landmarks that can provide an accurate localization of activation foci along the parahippocampal cortex and allow identification of subdivisions involved in the processing of spatial information.

Examining the neural impact of pediatric concussion: a scoping review of multimodal and integrative approaches using functional and structural MRI techniques.

PURPOSE OF REVIEW: This study presents the findings from a scoping review of recent, original research investigating changes in brain structure and/or function following pediatric concussion or mild traumatic brain injury (mTBI) using MRI and functional MRI techniques. RECENT FINDINGS: Our scoping review identified only five studies, two of which were focused specifically on sports-related concussion. A common finding across studies was that traditional structural methods such as anatomical T1, T2, and even susceptibility-weighted MRI failed to reveal abnormalities in brain structure following pediatric concussion/mTBI. Although data suggest alterations in brain function associated with concussion, correlation with changes in performance is inconsistently found, possibly because of the use of compensatory cerebral mechanisms or alternate pathways while the brain is still dysfunctional. SUMMARY: In conclusion, the literature describing neuroimaging investigations of pediatric concussion is too scarce to allow the formulation of definitive conclusions regarding the impact of concussion on the developing brain. There is a dire need for longitudinal, multisite investigations focused on a wider age range and recovery period.

Contributions of neuroimaging, balance testing, electrophysiology and blood markers to the assessment of sport-related concussion.

OBJECTIVE: To review the diagnostic tests and investigations used in the management of sports concussion, in the adult and paediatric populations, to (a) monitor the severity of symptoms and deficits, (b) track recovery and (c) advance knowledge relating to the natural history and neurobiology of the injury. DESIGN: Qualitative literature review of the neuroimaging, balance testing, electrophysiology, blood marker and concussion literature. INTERVENTION: PubMed and Medline databases were reviewed for investigations used in the management of adult and paediatric concussion, including structural imaging (computerised tomography, magnetic resonance imaging, diffusion tensor imaging), functional imaging (single photon emission computerised tomography, positron emission tomography, functional magnetic resonance imaging), spectroscopy (magnetic resonance spectroscopy, near infrared spectroscopy), balance testing (Balance Error Scoring System, Sensory Organization Test, gait testing, virtual reality), electrophysiological tests (electroencephalography, evoked potentials, event related potentials, magnetoencephalography, heart rate variability), genetics (apolipoprotein E4, channelopathies) and blood markers (S100, neuron-specific enolase, cleaved Tau protein, glutamate). RESULTS: For the adult and paediatric populations, each test has been classified as being: (1) clinically useful, (2) a research tool only or (3) not useful in sports-related concussion. CONCLUSIONS: The current status of the diagnostic tests and investigations is analysed, and potential directions for future research are provided. Currently, all tests and investigations, with the exception of clinical balance testing, remain experimental. There is accumulating research, however, that shows promise for the future clinical application of functional magnetic resonance imaging in sport concussion assessment and management.

Feedback and cognition in arm motor skill reacquisition after stroke.

BACKGROUND AND PURPOSE: A debated subject in stroke rehabilitation relates to the best type of training approach for motor recovery. First, we analyzed the effects of repetitive movement practice in 2 feedback conditions (knowledge of results [KR]; knowledge of performance, [KP]) on reacquisition of reaching. Second, we evaluated the impact of cognitive impairment on motor relearning ability. METHODS: A randomized controlled clinical trial was conducted in Montreal-area rehabilitation centers between 1998 and 2003 with 37 patients with chronic hemiparesis. Patients were randomly assigned to 3 groups: (1) KR (n=14) practiced a reaching task involving 75 repetitions per day, 5 days per week for 2 weeks, with 20% KR about movement precision; (2) KP (n=14) trained on the same task and schedule as KR but with faded KP about joint motions; and (3) control (C; n=9) practiced a nonreaching task. Physical (motor impairment, function) and kinematic (movement time, precision, segmentation, variability) variables were assessed before and after (immediately, 1 month) practice. Cognitive functions (memory, attention, mental flexibility, planning) were also evaluated. RESULTS: Kinematic gains in KR (precision) and KP (time, variability) exceeded those in C and depended on memory and mental flexibility deficits. In KP, more severely impaired patients made the most clinical gains (>2xC), which were related to memory and planning abilities. CONCLUSIONS: Use of KP during repetitive movement practice resulted in better motor outcomes. Stroke severity together with cognitive impairments are important factors for choosing motor rehabilitation interventions after stroke.

Tactile functions after cerebral hemispherectomy.

Patients that were hemispherectomized due to brain lesions early in life sometimes have remarkably well-preserved tactile functions on their paretic body half. This has been attributed to developmental neuroplasticity. However, the tactile examinations generally have been fairly crude, and subtle deficits may not have been revealed. We investigated monofilament detection and three types of tactile directional sensibility in four hemispherectomized patients and six healthy controls. Patients were examined bilaterally on the face, forearm and lower leg. Normal subjects were examined unilaterally. Following each test of directional sensibility, subjects were asked to rate the intensity of the stimulation. On the nonparetic side, results were almost always in the normal range. On the paretic side, the patients' capacity for monofilament detection was less impaired than their directional sensibility. Despite the disturbed directional sensibility on their paretic side the patients rated tactile sensations evoked by the stimuli, on both their paretic and nonparetic body halves, as more intense than normals. Thus, mechanisms of plasticity seem adequate for tactile detection and intensity coding but not for more complex tactile functions such as directional sensibility. The reason for the high vulnerability of tactile directional sensibility may be that it depends on spatially and temporally precise afferent information processed in a distributed cortical network.

Functional abnormalities in symptomatic concussed athletes: an fMRI study.

Our aim was to quantify with functional magnetic resonance imaging (fMRI) changes in brain activity in concussed athletes and compare the results with those of normal control subjects. Regional brain activations associated with a working memory task were obtained from a group of concussed athletes (15 symptomatic, 1 asymptomatic) and eight matched control subjects, using blood oxygen level dependent (BOLD) fMRI. The average percent signal change from baseline to working memory condition in each region of interest was computed. Symptomatic concussed athletes demonstrated task-related activations in some but not all the regions of interest, even when they performed as well as the control subjects. Furthermore, several concussed athletes had additional increases in activity outside the regions of interest, not seen in the control group. Quantitative analysis of BOLD signals within regions of interest revealed that, in general, concussed athletes had different BOLD responses compared to the control subjects. The task-related activation pattern of the one symptom-free athlete was comparable to that of the control group. We also repeated the study in one athlete whose symptoms had resolved. On the first study, when he was still symptomatic, less task-related activations were observed. On follow-up, once his symptoms had disappeared, the task-related activations became comparable to those of the control group. These results demonstrate the potential of fMRI, in conjunction with the working memory task, to identify an underlying pathology in symptomatic concussed individuals with normal structural imaging results.

Arm reaching improvements with short-term practice depend on the severity of the motor deficit in stroke.

The effects of short-term, constant practice on the kinematics of a multi-joint pointing movement were studied in the hemiparetic arm of 20 chronic patients with unilateral left cerebro-vascular accident (CVA) and in 10 age- and sex-matched healthy individuals. Practice consisted of a single session of 70 pointing movements made with the right arm. Movements were made from a target located beside the body to one in the contralateral workspace, in front of the body. Vision of the final hand position was allowed after every 5th trial. At the beginning of practice, stroke patients made slower, less precise and more segmented movements, characterised by smaller active ranges of elbow and shoulder motion, disrupted elbow-shoulder coordination, as well as greater trunk movement compared with healthy subjects. With practice, healthy subjects and some patients made faster and more precise movements. These tendencies were revealed only after many repetitions (up to 55 for those with severe hemiparesis), whereas changes in healthy individuals occurred after fewer trials (approximately 20). In addition, the patients decreased movement segmentation with practice. In healthy subjects, faster movement times may be attributed to better shoulder/elbow movement timing in the first half of the reach, whereas improvement of precision was not correlated with any changes in the movement variables. In patients, improvements were accomplished differently depending on arm motor severity. For some patients with mild-to-moderate clinical symptoms, practice resulted in better timing of shoulder/elbow movements with less trunk rotation in middle to late reach. Patients with more severe impairment also improved shoulder/elbow movement timing in mid-reach but used more compensatory trunk rotation. The results suggest that even one session of repetitive practice of a multi-joint pointing task leads to improvements in movement performance-based outcome measures, but the mechanisms of improvement may vary with the individual's level of motor impairment.

Stereoscopic processing in the human brain as a function of binocular luminance rivalry.

We investigated the neural substrates of a recent model of human stereodepth perception by obtaining measurements of regional cerebral blood flow (rCBF) using PET. Subjects experienced the perceptual properties of stereopsis by viewing rival-luminance stereograms displaying an identical random-dot pattern in their central portion while the backgrounds exhibited correspondent dots contrasting in black/white luminance. The stereoscopic vision induced by retinal luminance rivalry coincided with a significant elevation of rCBF in the dorsal visual pathway. Area V5 (MT) was activated bilaterally by the experimental condition while the remaining active loci were restricted to the right hemisphere. The neural sites that responded to this novel stereoscopic stimulus are similar to those activated by traditional stereograms containing horizontal disparities.

'Seeing' in the blind hemifield following hemispherectomy.

Destruction of the striate cortex has traditionally been thought to lead to permanent blindness in the contralateral visual field and to the dogma that this region is indispensable for vision in primates. For over 25 years now, evidence has been accumulating that hemianopic human subjects and monkeys possess wide-ranging residual visual capacities or 'blindsight' in the blind part of their visual field. For some researchers, isolated islands of the striate cortex have been associated with patches of degraded vision and made responsible for blindisight. Artefacts such as light scatter, criterion effects, macular sparing, eccentric fixation and minute eye movements have also been linked with the residual vision. For others, the fact that certain aspects of the visual information can be processed without the geniculostriate pathway suggests mediation by the visual subsystems such as extrastriate visual cortical areas which receive visual information via subcortical pathways, that escaped the cortical damage. Subjects who have had a whole cerebral hemisphere removed or disconnected (for the treatment of uncontrollable epilepsy) and who show residual vision in their blind field offer a remarkable opportunity to help clear the controversy regarding the neural substrate of blindsight. Because it is certain that no functional striate or extrastriate cortex remains on the ablated side, these subjects have contributed significantly to identifying the critical pathways involved in blindsight.

New frontiers in diagnostic imaging in concussive head injury.

Concussed athletes may have documented incapacitating postconcussive symptoms, neuropsychological deficits, and consequent important changes in their lives and sport, yet the majority of neuroimaging attempts reveal few findings to account for these signs and symptoms. In this paper, we explore new techniques in the neuroimaging of concussion including diffusion-weighted magnetic resonance imaging and functional brain imaging technology.

Central pain in a hemispherectomized patient.

We have examined a hemispherectomized patient who complained of touch-evoked pricking and burning pain in her paretic hand, especially when the hand was cold. Psychophysical examination showed that for the paretic side she confused cool and warm temperatures, and confirmed that she had a robust allodynia to brush stroking that was enhanced at a cold ambient temperature. Functional magnetic resonance imaging (fMRI) showed that during brush-evoked allodynia, brain structures implicated in normal pain processing (viz. posterior part of the anterior cingulate cortex, secondary somatosensory cortex, and prefrontal cortices) were activated. The fMRI findings thus indicate that the central pain in this patient was served by brain structures implicated in normal pain processing. Possible pathophysiological mechanisms include plasticity as well as thalamic disinhibition.

Cortical activation by tactile and painful stimuli in hemispherectomized patients.

Hemispherectomized patients are able to perceive tactile and painful stimuli on their nonparetic as well as paretic body halves. We have used functional MRI to study the cortical mechanisms underlying this preserved somatosensory capacity. Nonpainful brushing and painful heat were applied to the skin of the legs in four hemispherectomized patients and, for comparison, in four normal subjects. Cortical activation was studied with a 1.5 T scanner using a BOLD (blood oxygen level dependent) protocol. All patients rated both the brushing and the heat pain as almost equally intense on each leg and the ratings were similar to those in normals. Brushing on the nonparetic leg activated primary and secondary somatosensory cortices (S1 and S2) in all patients, similar to findings in normals. Brushing on the paretic leg activated S1 in two patients and S2 in one of these patients. Heat pain activated S2, insular cortex and anterior cingulate cortex to a similar degree for both legs, but the activation was weaker in the patients than in the normals. For the individual patient, there was generally no obvious correlation between cortical activation as studied with the BOLD technique and psychophysical performance. The findings from tactile stimulation of the nonparetic leg, that the activation was similar to the contralateral activation in normals, suggest that tactile information processing in the hemisphere contralateral to the stimulation is independent of the corpus callosum. In contrast, the pain activation for the nonparetic leg was weaker than in normals, suggesting that pain activation in the hemisphere contralateral to the stimulation is dependent on transcallosal information processing. The latter finding was corroborated by a subnormal capacity for pain localization on the nonparetic foot in two of the patients. The findings from stimulation of the paretic leg show that areas typically involved in the processing of tactile and painful stimuli can be activated by ipsilateral pathways directly from the periphery. The tactile-evoked ipsilateral S1 activation may be due to subcortical reorganization, since it was not observed in the normal subjects.

Sleep in right hemispherectomized patients: evidence of electrophysiological compensation.

OBJECTIVES: The goal of this study is to provide a better understanding of the role of the cortex in sleep's macro- and microstructure modulation. METHODS: Sleep architecture and phasic events were investigated in 4 patients having undergone right functional or anatomical hemispherectomy and 8 control subjects. Between-groups differences were assessed using the Wilcoxon-Mann-Whitney test. RESULTS: Findings provide evidence for overall similarity between patients' and control subjects' left hemispheric sleep architecture. In addition, results clearly indicate that it is possible to detect electrical activity over the operated side of a hemispherectomized patient's brain, even when resection of the hemi-cortex has been complete. Finally, findings provide evidence for similar left and right hemispheric relative spectral activities and for an increase in fast activity bands over the intact hemisphere in anatomical hemispherectomized patients. CONCLUSIONS: This study provides evidence that right hemispherectomy does not produce significant sleep architecture alterations as recorded over the intact hemisphere. In addition, residual activity detected over the operated side in anatomical hemispherectomized patients is interpreted as resulting from volume conduction originating from generators located in the intact hemisphere. Finally, there is strong evidence for electrophysiological compensation in the intact hemisphere following complete resection of the contralateral hemi-cortex.

Reorganisation of the visual cortex in callosal agenesis and colpocephaly.

Structural defects involving eloquent regions of the cerebral cortex may be accompanied by abnormal localisation of function. Using functional magnetic resonance imaging (fMRI), we studied the organisation of the visual cortex in a patient with callosal agenesis and colpocephaly, whose visual acuity and binocular visual fields were normal. The stimulus used was a moving grating confined to one hemifield, on a background of moving dots. In addition to activation patterns elicited by stimulation of each hemifield in the patient, the activation pattern was compared to that seen in six normal volunteers. fMRI demonstrated large scale reorganisation of visual cortical areas in the left hemisphere, and fewer activation foci were observed in both occipital lobes when compared with normal subjects.

Parallel visuomotor processing in the split brain: cortico-subcortical interactions.

We tested nine patients with callosal pathology in a simple reaction time task with and without redundant targets in the same or opposite visual hemifield. Four patients showed large facilitation (redundancy gain) in the presence of a redundant target, exceeding probability summation models (neural summation). Five patients showed redundancy gain not exceeding probability models. Violation of probability models was not associated with a specific type of callosal lesion. Neural summation, which probably occurs at collicular level, may be modulated by cortical activity. To test this hypothesis, we used functional MRI. During detection of redundant simultaneous targets, activations in the extrastriate cortex were observed in a patient with callosal agenesis and redundancy gain violating probability models, but not in a patient with callosal agenesis and redundancy gain not exceeding probability models. We conclude that cortical activity in the extrastriate cortex may be a modulating factor in the magnitude of the redundancy gain during parallel visuomotor transforms.

Somatosensory representation in patients who have undergone hemispherectomy: a functional magnetic resonance imaging study.

OBJECT: Removal or disconnection of an entire cerebral hemisphere is occasionally used to treat refractory seizures. Patients who have undergone a hemispherectomy provide useful models to study the reorganization of cortical somatosensory representation. This plasticity may be a consequence of the pathological lesion, the hemispherectomy itself, or both. METHODS: Three patients who had undergone hemispherectomy were studied with functional magnetic resonance (fMR) imaging. Responses to sensory stimulation in normal hands and hands opposite the lesioned hemisphere were studied. Multislice T2*-weighted gradient-echo echoplanar images were obtained using a 1.5-tesla MR imager. The activation condition consisted of somatosensory stimulation of the index finger. A T1-weighted anatomical MR image was acquired. The fMR and anatomical MR images were coregistered, and statistically significant activation foci (p < 0.01) were identified. Stimulation of the normal hand produced activation in the primary somatosensory cortex (SI) in all patients. Stimulation of the impaired hand resulted in activation of the ipsilateral parietal operculum (second somatosensory area [SII]) and posterior parietal lobe (Brodmann's Area 7) in all cases, but no activation was elicited in the SI in any patient. In addition, other areas within the ipsilateral frontal and parietal lobes were activated in some individuals. CONCLUSIONS: Residual somatosensory function in the hand opposite the lesioned hemisphere is mediated by the SII and other cortical regions in the intact hemisphere, without involvement of the SI.

History of Joubert syndrome and a 30-year follow-up of the original proband.

The 1960s were a period of great flowering in the recognition of neurologic disorders in children. The so-called ataxic cerebral palsies were an especially fertile field waiting for clarification. Congenital ataxia coupled with hyperpnea-apnea, abnormal eye movements, and retardation was identified as an autosomal-recessive syndrome eponimically associated with the senior author, Marie Joubert. The disorder, though rare, is increasingly recognized and a lay society dedicated to family support and research has been formed. In preparation for a recent symposium the original proband was re-examined 30 years later and the manifestations in adults clarified. Severe dysarthria was the most striking feature in this man, the hyperpnea-apnea had diminished, and the abnormal eye movements were less striking. Ataxia was still present but not severe. Poor judgment and borderline intelligence rounded out the clinical picture. Modern imaging has clarified, in part, the anatomic basis of this syndrome.

Activation of the remaining hemisphere following stimulation of the blind hemifield in hemispherectomized subjects.

We used functional magnetic resonance imaging (fMRI) to investigate the neural substrates mediating residual vision in the "blind" hemifield of hemispherectomized patients. The visual stimuli were semicircular gratings moving in opposite directions on a dynamic random-dot background. They were specifically constructed to eliminate intra- and extraocular light scatter and optimize the activation of extrastriate cortical areas and their subcortical relays. Multislice T2*-weighted gradient echo (GE) echoplanar imaging (EPI) images (TR/TE = 4 s/45 ms, flip angle 90 degrees ) were acquired during activation and baseline visual stimulation. An activation minus baseline subtraction was performed, and the acquired t statistic map transformed into the stereotaxic coordinate space of Talairach and Tournoux. In seven normal control subjects, right hemifield stimulation produced significant activation foci in contralateral V1/V2, V3/V3A, VP, and V5 (MT). Significant activation was also produced in homologous regions of the right occipital lobe with left hemifield stimulation. Stimulation of the intact hemifield in hemispherectomized patients resulted in activation of similar areas exclusively within the contralateral hemisphere. Stimulation of the anopic hemifield produced statistically significant activation in the ipsilateral occipital lobe (putative area V5 or MT) and areas V3/V3A in the only subject with blindsight. We conclude that the remaining hemisphere may contribute to residual visual functions in the blind hemifield of hemispherectomized patients, possibly through the collicular-pulvinar route since the activated areas are known to receive their afferents from these subcortical nuclei.

Residual vision in the blind field of hemidecorticated humans predicted by a diffusion scatter model and selective spectral absorption of the human eye.

The notion of blindsight was recently challenged by evidence that patients with occipital damage and contralateral field defects show residual islands of vision which may be associated with spared neural tissue. However, this possibility could not explain why patients who underwent the resection or disconnection of an entire cerebral hemisphere exhibit some forms of blindsight. We present here a model for the detection of intraocular scatter, which can account for human sensitivity values obtained in the blind field of hemidecorticated patients. The model demonstrates that, under controlled experimental conditions i.e. where the extraocular scatter is eliminated, Lambertian intraocular scatter alone can account for the visual sensitivities reported in these patients. The model also shows that it is possible to obtain a sensitivity in the blind field almost equivalent to that in the good field using the appropriate parameters. Finally, we show with in-vivo spectroreflectometry measurements made in the eyes of our hemidecorticated patients, that the relative drop in middle wavelength sensitivity generally obtained in the blind field of these patients can be explained by selective intraocular spectral absorption.