Changes in serial optical topography and TMS during task performance after constraint-induced movement therapy in stroke: a case study

The authors examined serial changes in optical topography in a stroke patient performing a functional task, as well as clinical and physiologic measures while undergoing constraint-induced therapy (CIT). A 73-year-old right hemiparetic patient, who had a subcortical stroke 4 months previously, received 2 weeks of CIT. During the therapy, daily optical topography imaging using near-infrared light was measured serially while the participant performed a functional key-turning task. Clinical outcome measures included the Wolf Motor Function Test (WMFT), Motor Activity Log (MAL), and functional key grip test. Transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) were also used to map cortical areas and hemodynamic brain responses, respectively. Optical topography measurement showed an overall decrease in oxy-hemoglobin concentration in both hemispheres as therapy progressed and the laterality index increased toward the contralateral hemisphere. An increased TMS motor map area was observed in the contralateral cortex following treatment. Posttreatment fMRI showed bilateral primary motor cortex activation, although slightly greater in the contralateral hemisphere, during affected hand movement. Clinical scores revealed marked improvement in functional activities. In one patient who suffered a stroke, 2 weeks of CIT led to improved function and cortical reorganization in the hemisphere contralateral to the affected hand.     

Motor cortex localization using functional MRI and transcranial magnetic stimulation.

OBJECTIVE: Congenital brain lesions producing focal seizures may be accompanied by reorganization of the areas responsible for motor and sensory functions within the brain due to a phenomenon that has been termed "neuronal plasticity." This can be studied using functional MRI (fMRI) and transcranial magnetic stimulation (TMS). Using either method, the motor cortex can be localized noninvasively, but to date there have been few studies correlating the level of agreement between the two techniques. METHODS: We used fMRI and TMS to localize the motor cortex in a young woman with intractable focal seizures, congenital left arm weakness, and a dysplastic right hemisphere on MRI. RESULTS: There was excellent agreement in the localization of motor representation for each hand. Both were predominantly located in the left hemisphere. fMRI also showed an area of posterior activation in the right hemisphere, but there was no evidence of descending corticospinal projections from this site using TMS, direct cortical stimulation, and Wada testing. CONCLUSIONS: Functional MRI (fMRI) and transcranial magnetic stimulation (TMS) were successfully used to localize cortical motor function before epilepsy surgery. Each technique demonstrated migration of motor function for the left hand to the left motor cortex. After resection of the dysplastic right precentral gyrus there was no permanent increase in weakness or disability. The two techniques are complementary; fMRI indicates all cortical areas activated by the motor task, whereas TMS identifies only those areas giving rise to corticospinal projections.     

Localization of the human frontal eye fields and motor hand area with transcranial magnetic stimulation and magnetic resonance imaging

We localized the neuroanatomical correlates for control of saccadic eye movements and for finger movements using a combined transcranial magnetic stimulation (TMS) and magnetic resonance imaging (MRI) approach. Two participants underwent TMS while performing an endogenous saccade task. The motor hand area was localized by TMS and the region anterior to it was mapped to identify the borders of a region where TMS produced delays in generating contralateral saccades. MRI scans were then obtained with fiducial markers placed over the motor hand area and 2 cm anterior to it, the common cortical region that produced saccadic delays in these two subjects. It was also shown that the structural anatomy of the hand area, physiologically defined by visible contractions of the contralateral hand following TMS, corresponded to the knob-like structure recently reported [18, 19]. These results demonstrate that TMS can be a precise, non-invasive tool for neuroanatomical mapping of cortical structures when combined with structural images of the brain.     

Cortical and subcortical brain effects of transcranial magnetic stimulation (TMS)-induced movement: an interleaved TMS/functional magnetic resonance imaging study.

BACKGROUND: To date, interleaved transcranial magnetic stimulation and functional magnetic resonance imaging (TMS/fMRI) studies of motor activation have not recorded whole brain patterns. We hypothesized that TMS would activate known motor circuitry with some additional regions plus some areas dropping out. METHODS: We used interleaved TMS/fMRI (11 subjects, three scans each) to elucidate whole brain activation patterns from 1-Hz TMS over left primary motor cortex. RESULTS: Both TMS (110% motor threshold) and volitional movement of the same muscles excited by TMS caused blood oxygen level-dependent (BOLD) patterns encompassing known motor circuitry. Additional activation was observed bilaterally in superior temporal auditory areas. Decreases in BOLD signal with unexpected post-task "rebounds" were observed for both tasks in the right motor area, right superior parietal lobe, and in occipital regions. Paired t test of parametric contrast maps failed to detect significant differences between TMS- and volition-induced effects. Differences were detectable, however, in primary data time-intensity profiles. CONCLUSIONS: Using this interleaved TMS/fMRI technique, TMS over primary motor cortex produces a whole brain pattern of BOLD activation similar to known motor circuitry, without detectable differences from mimicked volitional movement. Some differences may exist between time courses of BOLD intensity during TMS circuit activation and volitional circuit activation.     

PET-Based Confirmation of Orientation Sensitivity of TMS-Induced Cortical Activation in Humans

BackgroundCurrently, it is difficult to predict precise regions of cortical activation in response to transcranial magnetic stimulation (TMS). Most analytical approaches focus on applied magnetic field strength in the target region as the primary factor, placing activation on the gyral crowns. However, imaging studies support M1 targets being typically located in the sulcal banks.Objective/hypothesisTo more thoroughly investigate this inconsistency, we sought to determine whether neocortical surface orientation was a critical determinant of regional activation.MethodsMR images were used to construct cortical and scalp surfaces for 18 subjects. The angle (θ) between the cortical surface normal and its nearest scalp normal for ～50,000 cortical points per subject was used to quantify cortical location (i.e., gyral vs. sulcal). TMS-induced activations of primary motor cortex (M1) were compared to brain activations recorded during a finger-tapping task using concurrent positron emission tomographic (PET) imaging.ResultsBrain activations were primarily sulcal for both the TMS and task activations (P < 0.001 for both) compared to the overall cortical surface orientation. Also, the location of maximal blood flow in response to either TMS or finger-tapping correlated well using the cortical surface orientation angle or distance to scalp (P < 0.001 for both) as criteria for comparison between different neocortical activation modalities.ConclusionThis study provides further evidence that a major factor in cortical activation using TMS is the orientation of the cortical surface with respect to the induced electric field. The results show that, despite the gyral crown of the cortex being subjected to a larger magnetic field magnitude, the sulcal bank of M1 had larger cerebral blood flow (CBF) responses during TMS.     

Motor representation in patients rapidly recovering after stroke: a functional magnetic resonance imaging and transcranial magnetic stimulation study

OBJECTIVE: Neuroimaging studies have suggested an evolution of the brain activation pattern in the course of motor recovery after stroke. Initially poor motor performance is correlated with an recruitment of the uninjured hemisphere that continuously vanished until a nearly normal (contralateral) activation pattern is achieved and motor performance is good. Here we were interested in the early brain activation pattern in patients who showed a good and rapid recovery after stroke. METHODS: Ten patients with first-ever ischemic stroke affecting motor areas had to perform self-paced simple or more complex movements with the affected or the unaffected hand during functional magnetic resonance imaging (fMRI). The location and number of activated voxels above threshold were determined. To study possible changes in the cortical motor output map the amplitude of the motor evoked potentials (MEP) and the extent of the excitable area were determined using transcranial magnetic stimulation (TMS). RESULTS: The pattern of activation observed with movements of the affected and the unaffected hand was similar. In the simple motor task significant (P<0.05) increases were found in the primary motor cortex ipsilateral to the movement, the supplementary motor area and the cerebellar hemisphere contralateral to the movement during performance with the affected hand compared to movements with the unaffected hand. When comparing simple with more complex movements performed with either the affected or the unaffected hand, a further tendency to increased activation in motor areas was observed. The amplitude of MEPs obtained from the affected hemisphere was smaller and the extent of cortical output maps was decreased compared to the unaffected hemisphere; but none of the patients showed MEPs at the affected hand when the ipsilateral unaffected motor cortex was stimulated. CONCLUSIONS: Despite a rapid and nearly complete motor recovery the brain activation pattern was associated with increased activity in (bilateral) motor areas as revealed with fMRI. TMS revealed impaired motor output properties, but failed to demonstrate ipsilateral motor pathways. Successful recovery in our patients may therefore rely on the increased bilateral activation of existing motor networks spared by the injury.     

Controlling human striatal cognitive function via the frontal cortex

Cognitive flexibility is known to depend on the striatum. However, the striatum does not act in isolation to bias cognitive flexibility. In particular, cognitive flexibility also implicates the frontal cortex. Here we tested the hypothesis that the human frontal cortex controls cognitive flexibility by regulating striatal function via topographically specific frontostriatal connections. To this end, we exploited a repetitive transcranial magnetic stimulation (TMS) protocol over frontal cortex that is known to increase dopamine release in the striatum. This intervention was combined with functional magnetic resonance imaging to determine the functional and topographic specificity of its consequences at the whole brain level. Participants were scanned both before and after off-line TMS while performing a cognitive switching task that is known to depend on a specific striatal substructure, the putamen. Frontal stimulation perturbed task-specific functional signals in the putamen, while reducing fronto-striatal functional connectivity. There were no such effects of TMS over the medial parietal cortex. These data strengthen the hypothesis that cognitive flexibility involves topographic frontal control of striatal function.     

Exploring the physiological effects of double-cone coil TMS over the medial frontal cortex on the anterior cingulate cortex: an H2(15)O PET study

Transcranial magnetic stimulation (TMS) using a double-cone coil over the medial frontal cortex has the potential to clarify the function of the anterior cingulate cortex (ACC) in cognition, emotion and mood disorders. Following demonstration of disruption of performance on psychological tasks closely linked to cingulate function using this TMS technique, the current study aimed to directly measure the regional distribution of physiological effects of stimulation in the brain with H2(15)O PET. Experiment 1 assessed the effect of increasing numbers of pulse trains of TMS on regional cerebral blood flow (rCBF). Experiment 2 assessed the capacity of medial frontal TMS to modulate brain activity associated with the Stroop task using medial parietal TMS as a control site of stimulation. SPM99 analyses, using the ACC as a region of interest, revealed clusters of increased rCBF during medial frontal TMS in Brodmann area 24 and reduced rCBF in more ventral ACC, the latter occurring in both experiments. In a whole-brain analysis, striking changes in rCBF were observed distal to the ACC following medial frontal TMS. Although TMS reliably affected Stroop task performance in early trials, there was no interaction between TMS and Stroop condition in rCBF. Our results suggest that medial frontal TMS using the double-cone coil can affect ACC activity. However, a number of more distal cortical areas were also affected in these experiments. These additional changes may reflect either 'downstream' effects of altered cingulate cortex activity or direct effects of the coil.     

Basic mechanisms of TMS.

Transcranial magnetic stimulation (TMS) is now established as an important noninvasive measure for neurophysiologic investigation of the central and peripheral nervous systems in humans. Magnetic stimulation can be used for stimulating peripheral nerves with a similar mechanism of activation as for electrical stimulation. When TMS is applied to the cerebral cortex, however, some features emerge that distinguish it from transcranial electrical stimulation. One of the most important features is designated the D and I wave hypothesis, which is now widely accepted as a mechanism of TMS of the motor cortex. Transcranial electrical stimulation excites the pyramidal tract axons directly, either at the initial segment of the neuron or at proximal internodes in the subcortical white matter, giving rise to D (direct) waves, whereas TMS excites the pyramidal neurons transsynaptically, giving rise to I (indirect) waves. There are still other phenomena with mechanisms that remain to be elucidated. First, not only excitatory effects but also inhibitory effects can be elicited by TMS of the cerebral cortex (e.g., the silent period and intracortical inhibition). The inhibitory effect may also be used to investigate cerebral functions other than the motor cortex, such as the visual, sensory cortices, and the frontal eye field, from which no overt response like the motor evoked potential can be elicited. Second, there is an abundance of intraregional functional connectivities among different cortical areas that can also be revealed by TMS, or TMS in combination with neuroimaging techniques. Last, repetitive transcranial stimulation exerts a lasting effect on brain function even after the stimulation has ceased. With further investigation of the neural mechanisms of TMS, these techniques will open up new possibilities for investigating the physiologic function of the brain as well as opportunities for clinical application.     

A primer of magnetic stimulation as a tool for neuropsychology

Transcranial magnetic stimulation (TMS) offers the neuropsychologist a 'virtual lesion' method of investigating the effects of cortical dysfunction. Classical neuropsychology relies on patients with irreversible, and often diffuse brain lesions and these factors place limitations on the inferences that can be drawn about normal brain function. Thus the neuropsychologist is constrained by the extent to which the damaged brain undergoes reorganisation and by the inability to address questions regarding the timing of cognitive functions. TMS can disrupt cognitive functions for a few tens of milliseconds (although some effects of TMS can be seen for longer), with spatial resolution in the order of a centimetre and therefore allows one to study the role of brain areas without the masking effects of cortical reorganisation. The spatial and temporal resolutions are not unique to TMS but because TMS can be used as a temporary interference technique, it has a functional resolution with which one can address questions beyond the range of other neuroimaging and patient studies. Here we outline how TMS produces transitory 'lesion' effects, examine how the effects of stimulation spread in depth and breadth across the cortex and discuss the principles of the use of TMS in neuropsychology. Finally, we also itemise some issues of safety.     

Functional MRI of the immediate impact of transcranial magnetic stimulation on cortical and subcortical motor circuits

Recent studies indicate that the cortical effects of transcranial magnetic stimulation (TMS) may not be localized to the site of stimulation, but spread to other distant areas. Using echo-planar imaging with blood-oxygenation-level-dependent (BOLD) contrast at 3 Tesla, we measured MRI signal changes in cortical and subcortical motor regions during high-frequency (3.125 Hz) repetitive TMS (rTMS) of the left sensorimotor cortex (M1/S1) at intensities above and below the active motor threshold in healthy humans. The supra- and subthreshold nature of the TMS pulses was confirmed by simultaneous electromyographic monitoring of a hand muscle. Suprathreshold rTMS activated a network of primary and secondary cortical motor regions including M1/S1, supplementary motor area, dorsal premotor cortex, cingulate motor area, the putamen and thalamus. Subthreshold rTMS elicited no MRI-detectable activity in the stimulated M1/S1, but otherwise led to a similar activation pattern as obtained for suprathreshold stimulation though at reduced intensity. In addition, we observed activations within the auditory system, including the transverse and superior temporal gyrus, inferior colliculus and medial geniculate nucleus. The present findings support the notion that re-afferent feedback from evoked movements represents the dominant input to the motor system via M1 during suprathreshold stimulation. The BOLD MRI changes in motor areas distant from the site of subthreshold stimulation are likely to originate from altered synaptic transmissions due to induced excitability changes in M1/S1. They reflect the capability of rTMS to target both local and remote brain regions as tightly connected constituents of a cortical and subcortical network.     

Effects of visual information regarding tactile stimulation on the somatosensory cortical activation:a functional MRI study

Many studies have investigated the evidence for tactile and visual interactive responses to activation of various brain regions. However, few studies have reported on the effects of visuo-tactile multisensory inte-gration on the amount of brain activation on the somatosensory cortical regions. The aim of this study was to examine whether coincidental information obtained by tactile stimulation can affect the somatosensory cortical activation using functional MRI. Ten right-handed healthy subjects were recruited for this study. Two tasks (tactile stimulation and visuotactile stimulation) were performed using a block paradigm during fMRI scanning. In the tactile stimulation task, in subjects with eyes closed, tactile stimulation was applied on the dorsum of the right hand, corresponding to the proximal to distal directions, using a rubber brush. In the visuotactile stimulation task, tactile stimulation was applied to observe the attached mirror in the MRI chamber reflecting their hands being touched with the brush. In the result of SPM group analysis, we found brain activation on the somatosensory cortical area. Tactile stimulation task induced brain acti-vations in the left primary sensory-motor cortex (SM1) and secondary somatosensory cortex (S2). In the visuo-tactile stimulation task, brain activations were observed in the both SM1, both S2, and right posterior parietal cortex. In all tasks, the peak activation was detected in the contralateral SM1. We examined the ef-fects of visuo-tactile multisensory integration on the SM1 and found that visual information during tactile stimulation could enhance activations on SM1 compared to the tactile unisensory stimulation.     

A combined TMS/fMRI study of intensity-dependent TMS over motor cortex.

BACKGROUND: Transcranial magnetic stimulation (TMS) allows noninvasive stimulation of neurons using time-varying magnetic fields. Researchers have begun combining TMS with functional imaging to simultaneously stimulate and image brain activity. Recently, the feasibility of interleaving TMS with functional magnetic resonance imaging (fMRI) was demonstrated. This study tests this new method to determine if TMS at different intensities shows different local and remote activation. METHODS: Within a 1.5 Tesla (T) MRI scanner, seven adults were stimulated with a figure-eight TMS coil over the left motor cortex for thumb, while continuously acquiring blood oxygen level dependent (BOLD) echoplanar images. TMS was applied at 1 Hz in 18-second long trains delivered alternately at 110% and 80% of motor threshold separated by rest periods. RESULTS: Though the TMS coil caused some artifacts and reduced the signal to noise ratio (SNR), higher intensity TMS caused greater activation than lower, both locally and remotely. The magnitude (approximately 3% increase) and temporal onset (2 to 5 sec) of TMS induced blood flow changes appear similar to those induced using other motor and cognitive tasks. CONCLUSIONS: Though work remains in refining this potentially powerful method, combined TMS/fMRI is both technically feasible and produces measurable dose-dependent changes in brain activity.     

Persistent mirror movements for over sixty years: the underlying mechanisms in a cerebral palsy patient.

OBJECTIVE: To determine the mechanisms underlying the mirroring of distal movements in both upper and lower limbs present in one individual from birth. METHODS: Transcranial magnetic stimulation (TMS), magnetic resonance imaging (MRI), functional magnetic resonance imaging (fMRI), voluntary and reflexly evoked electromyograms (EMG) and force measurements were used to obtain information about the motor pathways responsible for the mirror movements. RESULTS: MRI showed a significant loss of brain tissue from one hemisphere and fMRI indicated a significant functional reorganization had taken place. An obligatory mirroring of voluntary movement on the sound side occurs on the affected side, but some independent movement can be produced on the affected side, if enabled by weak contractions on the sound side. TMS mapping revealed bilateral projections from one hemisphere and virtually absent projections from the primary motor cortex of the other hemisphere. Spinal reflexes were restricted to the stimulated side. Transcortical reflexes were evoked bilaterally from the sound side, but not from the affected side. CONCLUSIONS: The physiological and imaging data are consistent with a mirroring from the intact motor cortex via the supplementary motor area. SIGNIFICANCE: Mirror movements in this individual represent a major cortical reorganization and a partial solution to the neonatal loss of substantial amounts of brain tissue.     

Left dorso-lateral repetitive transcranial magnetic stimulation affects cortical excitability and functional connectivity,but does not impair cognition in major depression

PURPOSE: Transcranial magnetic stimulation (TMS) has been used for over a decade to investigate cortical function. More recently, it has been employed to treat conditions such as major depression. This study was designed to explore the effects of differential treatment parameters, such as stimulation frequency. In addition, the data were examined to determine whether a change in connectivity occurred following TMS. METHOD: Fifteen patients with major depression were entered into a combined imaging and treatment experiment with single photon emission computed tomography (SPECT) and repetitive transcranial magnetic stimulation (rTMS) over left dorso-lateral prefrontal cortex (DLPFC). Brain perfusion during a verbal fluency task was compared between pre- and poststimulation conditions. Patients were then treated with 80% of motor threshold for a total of 10 days, using 5000 stimuli at 5, 10 or 20 Hz. Tests of cortical excitability and neuropsychological tests were done throughout the trial. FINDINGS: Patients generally improved with treatment. There was no perceptible difference between stimulation frequencies, which may have reflected low study power. An increase in rostral anterior cingulate activation after the treatment day was associated with increased functional connectivity in the dorso-lateral frontal loop on the left and the limbic loop on both sides. No noticeable deterioration in neuropsychological function was observed. CONCLUSION: TMS at the stimulation frequencies used seems to be safe over a course of 5000 stimuli. It appears to have an activating effect in anterior limbic structures and increase functional connectivity in the neuroanatomical networks under the stimulation coil within an hour of stimulation.     

Transcranial Magnetic Stimulation in the investigation and treatment of schizophrenia: a review

Transcranial Magnetic Stimulation (TMS) is a non-invasive method of stimulating the brain that is increasingly being used in neuropsychiatric research and clinical psychiatry. This review examines the role of TMS in schizophrenia research as a diagnostic and a therapeutic resource. After a brief overview of TMS, we describe the application of TMS to schizophrenia in studies of cortical excitability and inhibition, and we discuss the potential confounding role of neuroleptic medications. Based on these studies, it appears that some impairment of cortical inhibition may be present in schizophrenic subjects. We then review attempts to employ TMS for treating different symptoms of schizophrenia. Some encouraging results have been obtained, such as the reduction of auditory hallucinations after slow TMS over auditory cortex and an improvement of psychotic symptoms after high frequency TMS over left prefrontal cortex. However, these results need to be confirmed using better placebo conditions. Future studies are likely to employ TMS in combination with functional brain imaging to examine the effects produced by the stimulated area on activity in other brain regions. Such studies may reveal impaired effective connectivity between specific brain areas, which could identify these regions as targets for selective stimulation with therapeutic doses of TMS.     

Transcranial magnetic stimulation in migraine: a review of facts and controversies

There is compelling evidence that cortical excitability is modified in migraine patients between attacks. Transcranial magnetic stimulation (TMS) is a non-invasive tool to investigate this abnormality. Repetitive transcranial magnetic stimulation (rTMS) activates the underlying cortex at high, but inhibits it at low stimulation frequencies. This is a review of published results obtained in migraineurs with TMS and rTMS over motor or visual cortices. Prevalence and/or threshold data of phosphenes induced by single pulse TMS of the visual cortex are contradictory, some favouring increased, others decreased interictal excitability. The discrepancies may be due to differences in methodology and poor reliability of phosphene reporting. In a recent rTMS study of the occipital cortex we have found evidence in favour of an interictal decrease of the preactivation excitability level by using amplitude of visual evoked potentials and its habituation during sustained stimulation as indices of cortical excitability. The hypothesis of increased cortical excitability, taken in its strict physiological sense of a decreased response threshold and/or an increased response to a single suprathreshold stimulus, may thus not be any longer tenable. The long lasting effects of rTMS allow in future studies to assess metabolic changes of the cortex and subcortical structures with functional imaging methods and to explore novel therapeutic strategies for migraine.     

PreSMA stimulation changes task‐free functional connectivity in the fronto‐basal‐ganglia that correlates with response inhibition efficiency

Previous work using transcranial magnetic stimulation (TMS) demonstrated that the right presupplementary motor area (preSMA), a node in the fronto‐basal‐ganglia network, is critical for response inhibition. However, TMS influences interconnected regions, raising the possibility of a link between the preSMA activity and the functional connectivity within the network. To understand this relationship, we applied single‐pulse TMS to the right preSMA during functional magnetic resonance imaging when the subjects were at rest to examine changes in neural activity and functional connectivity within the network in relation to the efficiency of response inhibition evaluated with a stop‐signal task. The results showed that preSMA‐TMS increased activation in the right inferior‐frontal cortex (rIFC) and basal ganglia and modulated their task‐free functional connectivity. Both the TMS‐induced changes in the basal‐ganglia activation and the functional connectivity between rIFC and left striatum, and of the overall network correlated with the efficiency of response inhibition and with the white‐matter microstructure along the preSMA–rIFC pathway. These results suggest that the task‐free functional and structural connectivity between the rIFCop and basal ganglia are critical to the efficiency of response inhibition. Hum Brain Mapp 37:3236–3249, 2016. © 2016 Wiley Periodicals, Inc.     

Intraoperative infrared functional imaging of human brain

We hypothesized that it would be possible to detect the distribution of cortical activation by using a sensitive, rapid, high-resolution infrared imaging technique to monitor changes in local cerebral blood flow induced by changes in focal cortical metabolism. In a prospective study, we recorded in 21 patients the emission of infrared radiation from the exposed human cerebral cortex at baseline, during language and motor tasks, and during stimulation of the contralateral median nerve using an infrared camera (sensitivity 0.02 degrees C). The language and sensorimotor cortex was identified by standard mapping methods (cortical stimulation, median nerve somatosensory-evoked potential, functional magnetic resonance imaging), which were compared with infrared functional localization. The temperature gradients measured during surgery are dominated by changes in local cerebral blood flow associated with evoked functional activation. The distribution of the evoked temperature changes overlaps with, but extends beyond, functional regions identified by standard mapping techniques. The distribution observed via infrared mapping is consistent with distributed and complex functional representation of the cerebral cortex, rather than the traditional concept of discrete functional loci demonstrated by brief cortical stimulation during surgery and by noninvasive functional imaging techniques. By providing information on the spatial and temporal patterns of sensory-motor and language representation, infrared imaging may prove to be a useful approach to study brain function.