Circadian modulation of GABA-mediated cortical inhibition

Circadian rhythms exert powerful influence on various aspects of human physiology and behavior. Here, we tested changes of human cerebral cortex excitability over the course of the day with transcranial magnetic stimulation (TMS). At different times of the day, intracortical and corticospinal excitability of the primary motor cortex (M1) was evaluated in 15 healthy subjects by TMS of left M1. While motor thresholds, short-interval intracortical inhibition and facilitation and input/output curves remained unchanged, we found that a specific form of γ-aminobutyric acid (GABA)-mediated intracortical inhibition, revealed by long-interval intracortical inhibition and cortical silent periods, progressively decreased during the course of the day. Additional experiments demonstrated that morning inhibition persisted irrespective of previous sleep or sleep deprivation. Corticotropin-releasing hormone (CRH) infusions in the evening lead to morning cortisol levels but did not restore levels of morning inhibition, whereas suppression of endogenous CRH release by repeated oral dexamethasone intake over 24 h prevented morning inhibition. The findings suggest a specific modulation of GABAergic motor cortex inhibition within the circadian cycle, possibly linked to the CRH system, and may indicate a neurobiological basis for variable neuroplasticity over the course of the day.     

Dorsal premotor cortex exerts state-dependent causal influences on activity in contralateral primary motor and dorsal premotor cortex

During voluntary action, dorsal premotor cortex (PMd) may exert influences on motor regions in both hemispheres, but such interregional interactions are not well understood. We used transcranial magnetic stimulation (TMS) concurrently with event-related functional magnetic resonance imaging to study such interactions directly. We tested whether causal influences from left PMd upon contralateral (right) motor areas depend on the current state of the motor system, involving regions engaged in a current task. We applied short bursts (360 ms) of high- or low-intensity TMS to left PMd during single isometric left-hand grips or during rest. TMS to left PMd affected activity in contralateral right PMd and primary motor cortex (M1) in a state-dependent manner. During active left-hand grip, high (vs. low)-intensity TMS led to activity increases in contralateral right PMd and M1, whereas activity decreases there due to TMS were observed during no-grip rest. Analyses of condition-dependent functional coupling confirmed topographically specific stronger coupling between left PMd and right PMd (and right M1), when high-intensity TMS was applied to left PMd during left-hand grip. We conclude that left PMd can exert state-dependent interhemispheric influences on contralateral cortical motor areas relevant for a current motor task.     

Role of the ipsilateral primary motor cortex in controlling the timing of hand muscle recruitment

The precise contribution of the ipsilateral primary motor cortex (iM1) to hand movements remains controversial. To address this issue, we elicited transient virtual lesions of iM1 by means of transcranial magnetic stimulation (TMS) in healthy subjects performing either a grip-lift task or a step-tracking task with their right dominant hand. We found that, irrespective of the task, a virtual lesion of iM1 altered the timing of the muscle recruitment. In the grip-lift task, this led to a less coordinated sequence of grip and lift movements and in the step-tracking task, to a perturbation of the movement trajectory. In the step-tracking task, we have demonstrated that disrupting iM1 activity may, depending on the TMS delay, either advance or delay the muscle recruitment. The present study suggests that iM1 plays a critical role in hand movements by contributing to the setting of the muscle recruitment timing, most likely through either inhibitory or facilitatory transcallosal influences onto the contralateral M1 (cM1). iM1 would therefore contribute to shape precisely the muscular command originating from cM1.     

Transcranial magnetic stimulation of primary motor cortex affects mental rotation

Neuroimaging studies have shown that motor structures are activated not only during overt motor behavior but also during tasks that require no overt motor behavior, such as motor imagery and mental rotation. We tested the hypothesis that activation of the primary motor cortex is needed for mental rotation by using single- pulse transcranial magnetic stimulation (TMS). Single-pulse TMS was delivered to the representation of the hand in left primary motor cortex while participants performed mental rotation of pictures of hands and feet. Relative to a peripheral magnetic stimulation control condition, response times (RTs) were slower when TMS was delivered at 650 ms but not at 400 ms after stimulus onset. The magnetic stimulation effect at 650 ms was larger for hands than for feet. These findings demonstrate that (i) activation of the left primary motor cortex has a causal role in the mental rotation of pictures of hands; (ii) this role is stimulus-specific because disruption of neural activity in the hand area slowed RTs for pictures of hands more than feet; and (iii) left primary motor cortex is involved relatively late in the mental rotation process.     

Stimulus repetition probability does not affect repetition suppression in macaque inferior temporal cortex

Recent human functional magnetic resonance imaging studies (Summerfield C, Trittschuh EH, Monti JM, Mesulam MM, Egner T. 2008. Neural repetition suppression reflects fulfilled perceptual expectations. Nat Neurosci. 11:1004-1006.) showed that adaptation or repetition suppression is affected by contextual factors related to perceptual expectations, suggesting that adaptation results from a fulfillment of perceptual expectation or a reduction in prediction error. This view contrasts with the bottom-up fatigue or sharpening mechanisms of adaptation proposed in single-cell studies. We examined whether stimulus repetition probability affects adaptation of spiking activity and local field potentials (LFPs) in macaque inferior temporal (IT) cortex, using a protocol similar to that of Summerfield et al. Monkeys were exposed to 2 randomly interleaved trials, each consisting of either 2 identical (rep trial) or 2 different stimuli (alt trial). Trials were presented in repetition (rep) blocks consisting of 75% of rep trials and 25% of alt trials or in alternation (alt) blocks having opposite repetition probabilities. For both spiking and LFP activities, the stimulus-selective adaptation did not differ significantly between rep and alt blocks. The number of preceding rep or alt trials and the trial position within a block did not affect adaptation. This absence of any effect of stimulus repetition probability on adaptation suggests that adaptation in IT is not caused by contextual factors related to perceptual expectation.     

Effects of repetitive transcranial magnetic stimulation on movement-related cortical activity in humans

Several lines of evidence suggest that low-rate repetitive transcranial magnetic stimulation (rTMS) of the motor cortex at 1 Hz reduces the excitability of the motor cortex and produces metabolic changes under and at a distance from the stimulated side. Therefore, it has been suggested that rTMS may have beneficial effects on motor performance in patients with movement disorders. However, it is still unknown in what way these effects can be produced. The aim of the present study is to investigate whether rTMS of the motor cortex (15 min at 1 Hz) is able to modify the voluntary movement related cortical activity, as reflected in the Beretischaftspotential (BP), and if these changes are functionally relevant for the final motor performance. The cortical movement-related activity in a typical BP paradigm of five healthy volunteers has been recorded using 61 scalp electrodes, while subjects performed self-paced right thumb oppositions every 8-20 s. After a basal recording, the BP was recorded in three different conditions, counterbalanced across subjects: after rTMS stimulation of the left primary motor area (M1) (15 min, 1 Hz, 10% above motor threshold), after 15 min of sham rTMS stimulation and following 15 min of voluntary movements performed with spatio-temporal characteristics similar to those induced by TMS. The tapping test was used to assess motor performance before and after each condition. Only movement-related trials with similar electromyographic (onset from muscular 'silence') and accelerometric patterns (same initial direction and similar amplitudes) were selected for computing BP waveforms. TMS- evoked and self-paced thumb movements had the same directional accelerometric pattern but different amplitudes. In all subjects, the real rTMS, but neither sham stimulation nor prolonged voluntary movements, produced a significant amplitude decrement of the negative slope of the BP; there was also a shortening of the BP onset time in four subjects. The effect was topographically restricted to cortical areas which were active in the basal condition, irrespective of the basal degree of activation at every single electrode. No changes in the tapping test occurred. These findings suggest that rTMS of the motor cortex at 1 Hz may interfere with the movement related brain activity, probably through influence on cortical inhibitory networks.     

Dorsolateral prefrontal cortex prevents short-latency saccade and vergence: a TMS study

This study explores whether vergence eye movements along the median plane can be triggered with short latencies, and the role of the dorsolateral prefrontal cortex (DLPFC) in controlling such movements. We used a gap paradigm and applied transcranial magnetic stimulation (TMS) in 10 humans making saccades or vergence. TMS over the motor cortex had no effect on any eye movement parameter. TMS over DLPFC influenced eye movement initiation but not their metrics. TMS over the right DLPFC accelerated the triggering of saccades bilaterally but did not influence divergence. TMS over the left DLPFC speeded up the triggering of ipsilateral saccades and exacerbated the anticipatory mode of triggering of divergence. For convergence, TMS effects were mild: rightward TMS increased the proportion of short latencies but failed to shorten the group mean latency; leftward TMS influenced triggering in some individuals only. For saccades and convergence under TMS, some subjects showed an emerging population of short latencies in their latency distribution. Horizontal saccadic intrusions (80% of trials) and vertical saccades (recorded in one subject) intruding on vergence were unlikely to assist vergence triggering. We conclude that the prefrontal mechanisms underlying voluntary eye movement control are similar for saccades and vergence although some specificities exist.     

Descending systems translate transient cortical commands into a sustained muscle activation signal

Controlling motor actions requires online adjustments of time-varying parameters. Although numerous studies have attempted to identify the parameters coded in different motor sites, the relationships between the temporal profile of neuronal responses and the dynamics of motor behavior remain poorly understood in particular because motor parameters such as force and movement direction often change over time. We studied time-dependent coding of cortical and spinal neurons in primates performing an isometric wrist task with an active hold period, which made it possible to segregate motor behavior into its phasic and sustained components. Here, we show that cortical neurons transiently code motor-related parameters when actively acquiring a goal, whereas spinal interneurons provide persistent information regarding maintained torque level and posture. Moreover, motor cortical neurons differed substantially from spinal neurons with regard to the evolvement of parameter-specific coding over the course of a trial. These results suggest that the motor cortex and spinal cord use different control policies: Cortical neurons produce transient motor commands governing ensuing actions, whereas spinal neurons exhibit sustained coding of ongoing motor states. Hence, motor structures downstream to M1 need to integrate cortical commands to produce state-dependent spinal firing.     

Rapid face-selective adaptation of an early extrastriate component in MEG

Adaptation paradigms are becoming increasingly popular for characterizing visual areas in neuroimaging, but the relation of these results to perception is unclear. Neurophysiological studies have generally reported effects of stimulus repetition starting at 250-300 ms after stimulus onset, well beyond the latencies of components associated with perception (100-200 ms). Here we demonstrate adaptation for earlier evoked components when 2 stimuli (S1 and S2) are presented in close succession. Using magnetoencephalography, we examined the M170, a "face-selective" response at 170 ms after stimulus onset that shows a larger response to faces than to other stimuli. Adaptation of the M170 occurred only when stimuli were presented with relatively short stimulus onset asynchronies (< 800 ms) and was larger for faces preceded by faces than by houses. This face-selective adaptation is not merely low-level habituation to physical stimulus attributes, as photographic, line-drawing, and 2-tone face images produced similar levels of adaptation. Nor does it depend on the amplitude of the S1 response: adaptation remained greater for faces than houses even when the amplitude of the S1 face response was reduced by visual noise. These results indicate that rapid adaptation of early, short-latency responses not only exists but also can be category selective.     

Memory formation in the motor cortex ipsilateral to a training hand

Cortical reorganization within the primary motor cortex (M1) contralateral to a practicing hand has been extensively investigated. The extent to which the ipsilateral M1 participates in these plastic changes is not known. Here, we evaluated the influence of unilateral hand practice on the organization of the M1 ipsilateral and contralateral to the practicing hand in healthy human subjects. Index finger movements elicited by single-pulse transcranial magnetic stimulation (TMS) delivered to each M1 were evaluated before and after practice of unilateral voluntary index finger abduction motions. Practice increased the proportion and acceleration of TMS-evoked movements in the trained direction and the amplitude of motor-evoked potentials (MEPs) in the abduction agonist first dorsal interosseous (FDI) muscle in the practicing hand and decreased the proportion and acceleration of TMS-evoked abduction movements and MEP amplitudes in the abduction agonist FDI in the opposite resting hand. Our findings indicate that unilateral hand practice specifically weakened the representation of the practiced movement in the ipsilateral M1 to an extent proportional to the strengthening effect in the contralateral M1, a result that varied with the practicing hand's position. These results suggest a more prominent involvement of interacting bilateral motor networks in motor memory formation and probably acquisition of unimanual motor skills than previously thought.     

Dissociating the roles of the cerebellum and motor cortex during adaptive learning: the motor cortex retains what the cerebellum learns

Adaptation to a novel visuomotor transformation has revealed important principles regarding learning and memory. Computational and behavioral studies have suggested that acquisition and retention of a new visuomotor transformation are distinct processes. However, this dissociation has never been clearly shown. Here, participants made fast reaching movements while unexpectedly a 30-degree visuomotor transformation was introduced. During visuomotor adaptation, subjects received cerebellar, primary motor cortex (M1) or sham anodal transcranial direct current stimulation (tDCS), a noninvasive form of brain stimulation known to increase excitability. We found that cerebellar tDCS caused faster adaptation to the visuomotor transformation, as shown by a rapid reduction of movement errors. These findings were not present with similar modulation of visual cortex excitability. In contrast, tDCS over M1 did not affect adaptation, but resulted in a marked increase in retention of the newly learnt visuomotor transformation. These results show a clear dissociation in the processes of acquisition and retention during adaptive motor learning and demonstrate that the cerebellum and primary motor cortex have distinct functional roles. Furthermore, they show that is possible to enhance cerebellar function using tDCS.     

Assessing the functional status of the motor system in brain tumor patients using transcranial magnetic stimulation

Background

Transcranial magnetic stimulation (TMS) is being used in the pre-operative diagnostics of patients with tumors in or near the motor cortex. Although the main purpose of TMS in such patients is to map the functional areas of the motor cortex in spatial relation to the tumor, TMS also provides some numerical neurophysiological measurements of the functional status of the patient’s motor system. The aim of this paper is to provide reference values for these neurophysiological measurements from a large and varied clinical sample.

Methods

TMS was used in the pre-operative work-up of patients with various types of tumors in or near the motor cortex during a 3-year period. Data was collected prospectively in 100 patients, yet this is a post hoc report.

Results

Patient characteristics had no influence on the neurophysiological parameters. The response latency time was almost never different in the tumorous versus healthy hemisphere, so clinicians should be suspicious if they find interhemispheric differences for latency. A high interhemispheric ratio of resting motor threshold (RMT) or a low interhemispheric ratio of motor evoked potential (MEP) amplitude appear to suggest immanent deterioration of the patient’s motor status.

Conclusion

In addition to topographic cortical mapping, TMS also serves as a neurophysiological assessment of the functional status of the patient’s motor system. The results presented here provide clinicians with a set of reference values to contextualize findings in their own tumor patients. Further research is still needed to better understand the full clinical relevance of these neurophysiological parameters.     

Refined myoelectric control in below-elbow amputees using artificial neural networks and a data glove

PURPOSE: To develop a system for refined motor control of artificial hands based on multiple electromyographic (EMG) recordings, allowing multiple patterns of hand movements. METHODS: Five subjects with traumatic below-elbow amputations and 1 subject with a congenital below- elbow failure of formation performed 10 imaginary movements with their phantom hand while surface electrodes recorded the EMG data. In a training phase a data glove with 18 degrees of freedom was used for positional recording of movements in the contralateral healthy hand. These movements were performed at the same time as the imaginary movements in the phantom hand. An artificial neural network (ANN) then could be trained to associate the specific EMG patterns recorded from the amputation stump with the analogous specific hand movements synchronously performed in the healthy hand. The ability of the ANN to predict the 10 imaginary movements offline, when they were reflected in a virtual computer hand, was assessed and calculated. RESULTS: After the ANN was trained the subjects were able to perform and control 10 hand movements in the virtual computer hand. The subjects showed a median performance of 5 types of movement with a high correlation with the movement pattern of the data glove. The subjects seemed to relearn to execute motor commands rapidly that had been learned before the accident, independent of how old the injury was. The subject with congenital below-elbow failure of formation was able to perform and control several hand movements in the computer hand that cannot be performed in a myoelectric prosthesis (eg, opposition of the thumb). CONCLUSIONS: With the combined use of an ANN and a data glove, acting in concert in a training phase, amputees rapidly can learn to execute several imaginary movements in a virtual computerized hand, this opens promising possibilities for motor control of future hand prostheses.     

Hemangioma of the prostate - an unusual cause of lower urinary tract symptoms: Case report

Background

Ureteral injury occurs in less than 1% of blunt abdominal trauma cases, partly because the ureters are relatively well protected in the retroperitoneum. Bilateral ureteral injury is extremely rare, with only 10 previously reported cases. Diagnosis may be delayed if ureteric injury is not suspected, and delay of 36 hours or longer has been observed in more than 50% of patients with ureteric injury following abdominal trauma, leading to increased morbidity.

Case presentation

A 29-year-old man was involved in a highway motor vehicle collision and was ejected from the front passenger seat even though wearing a seatbelt. He was in a preshock state at the scene of the accident. An intravenous line and left thoracic drain were inserted, and he was transported to our hospital by helicopter. Whole-body, contrast-enhanced computed tomography (CT) scan showed left diaphragmatic disruption, splenic injury, and a grade I injury to the left kidney with a retroperitoneal haematoma. He underwent emergency laparotomy. The left diaphragmatic and splenic injuries were repaired. Although a retroperitoneal haematoma was observed, his renal injury was treated conservatively because the haematoma was not expanding. In the intensive care unit, the patient's haemodynamic state was stable, but there was no urinary output for 9 hours after surgery. Anuresis prompted a review of the abdominal x-ray which had been performed after the contrast-enhanced CT. Leakage of contrast material from the ureteropelvic junctions was detected, and review of the repeat CT scan revealed contrast retention in the perirenal retroperitoneum bilaterally. He underwent cystoscopy and bilateral retrograde pyelography, which showed bilateral complete ureteral disruption, preventing placement of ureteral stents. Diagnostic laparotomy revealed complete disruption of the ureteropelvic junctions bilaterally. Double-J ureteral stents were placed bilaterally and ureteropelvic anastomoses were performed. The patient's postoperative progress was satisfactory and he was discharged on the 23^rd day.

Conclusion

Diagnosis of ureteral injury was delayed, although delayed phase contrast-enhanced CT and abdominal x-rays performed after CT revealed the diagnosis early. Prompt detection and early repair prevented permanent renal damage and the necessity for nephrectomy.     

Interhemispheric transmission of visuomotor information for motor implementation

Using transcranial magnetic stimulation (TMS), we addressed the contribution of both hemispheres to the visuomotor control of each hand. The subjects had to press one of two buttons as quickly as possible after the go-signal. A precue preceding this conveyed full, partial or no advance information (hand and/or button), such that reaction time (RT) shortened with increasing amount of information. We gave TMS over each hemisphere at various time intervals (100-350 ms) after the go-signal and before the expected onset of response, and measured its effect on RT, movement time (MT) and error rate. At short intervals (100-200 ms), left hemisphere TMS delayed RT and prolonged MT of both hands, while right hemisphere TMS delayed RT only of the right hand, without affecting error rates. At long intervals (250-350 ms), TMS produced slightly more pronounced RT delays of the contralateral hand. RT was delayed more if the precues were less informative. The results suggest the importance of interhemispheric transmission of visuomotor information for motor implementation. The right hemisphere may play a role mainly in calculating target and effector information, determining RT, while the left hemisphere may play a role in elaborating the motor program and determining MT.     

Comparison of cardiac output measurements between NICO and the pulmonary artery catheter during repeat surgery for total hip replacement

OBJECTIVE: The aim of this study was to compare cardiac output measurements of the non-invasive cardiac output and the pulmonary artery catheter during repeat surgery for hip replacement. METHODS: In this prospective observational study, patients undergoing repeat hip surgery who needed a pulmonary artery catheter were included. A standard protocol was followed for induction, endotracheal intubation and maintenance of anaesthesia (sufentanil, etomidate, sevoflurane, cisatracurium). After endotracheal intubation, the non-invasive cardiac output was connected and a pulmonary artery catheter was inserted. Data were collected every 3 min until patients were extubated. RESULTS: Ten patients were included and 2455 points of comparison recorded. Cardiac output from the pulmonary artery catheter varied from 1.7 to 8.9 L min(-1) (mean 4.1 L min(-1)) and the non-invasive cardiac output (using averaging mode) from 1.7 to 8.0 L min(-1) (mean 3.7 L min(-1)). There was a significant correlation between them (P < 0.01; bias 0.3 L min(-1); limits of agreement +1.9 and -2.5 L min(-1)), although these differed between patients. CONCLUSION: The perioperative bias was small and the non-invasive cardiac output slightly underestimated cardiac output intraoperatively compared to the pulmonary artery catheter. The bias was smaller when mean cardiac output was below 3 L min(-1). Core temperature between 34.4 degrees C and 37.6 degrees C had no influence on the differences.     

Intravesical Gemcitabine: State of the Art

Intravesical gemcitabine has been tested in several phase 1 studies. The 2000-mg dose of gemcitabine in 50 or 100 ml normal saline when administered intravesically for up to 2 h once a week for 6 wk has unremarkable systemic and local side effects; therefore, this schedule should be considered the most convenient.Phase 2 studies have assessed the activity of intravesical gemcitabine on a marker lesion in intermediate-risk superficial bladder cancers (SBCs), showing complete responses in up to 60% of cases. Few attempts have been made to test the activity of intravesical gemcitabine in high-risk SBC, achieving unexpected complete responses in carcinoma in situ refractory to Bacillus Calmette-Guérin. Initial trials have also documented “clinically relevant” responses in prophylaxis.The current level of evidence indicates that gemcitabine possesses clinical activity, but further confirmation is awaited from additional exploratory phase 2 and, preferably, phase 3 trials.     

Prognostic value of FMRI in recovery of hand function in subcortical stroke patients

The first objective of the study was to determine whether functional magnetic resonance imaging (fMRI) signal was correlated with motor performance at different stages of poststroke recovery. The second objective was to assess the existence of prognostic factors for recovery in early functional MR images. Eight right-handed patients with pure motor deficit secondary to a first lacunar infarct localized on the pyramidal tract were included. This study concerned moderately impaired patients and recovery of handgrip strength and finger-tapping speed. The fMRI task was a calibrated flexion-extension movement. Ten healthy subjects served as a control group. The intensity of the activation in the "classical" motor network (ipsilesional S1M1, ipsilesional ventral premotor cortex [BA 6], contralesional cerebellum) 20 days after stroke was indicative of the performance (positive correlation). The cluster in M1 was posterior and circumscribed to BA 4p. No area was associated with bad performance (negative correlation). No correlation was found 4 and 12 months after stroke. Prognosis factors were evidenced. The higher early the activation in the ipsilesional M1 (BA 4p), S1, and insula, the better the recovery 1 year after stroke. Although the lesions partly deefferented the primary motor cortex, patients who activated the posterior primary motor cortex early had a better recovery of hand function. This suggests that there is benefit in increasing ipsilesional M1 activity shortly after stroke as a rehabilitative approach in mildly impaired patients.     

Current status of clinical trials for acute spinal cord injury

Acute spinal cord injury (ASCI) occurs as a result of physical disruption of spinal cord axons through the epicenter of injury leading to deficits in motor, sensory, and autonomic function. This is a debilitating neurological disorder common in young adults that often requires life-long therapy and rehabilitative care, placing a significant burden on our healthcare system. While no cure exists, research has identified various pharmacological compounds that specifically antagonize primary and secondary mechanisms contributing to the etiology of ASCI. Several compounds including methylprednisolone (MPSS), GM-1 ganglio-side, thyrotropin releasing hormone (TRH), nimodipine, and gacyclidine have been tested in prospective randomized clinical trials of ASCI. MPSS and GM-1 ganglioside have shown evidence of modest benefits. Clearly trials of improved neuroprotective agents are required. Promising potential therapies for ASCI include riluzole, minocycline, erythropoietin, and the fusogen polyethylene glycol, as well as mild hypothermia.     

Imaging the brain activity changes underlying impaired visuospatial judgments: simultaneous FMRI, TMS, and behavioral studies

Damage to parietal cortex impairs visuospatial judgments. However, it is currently unknown how this damage may affect or indeed be caused by functional changes in remote but interconnected brain regions. Here, we applied transcranial magnetic stimulation (TMS) to the parietal cortices during functional magnetic resonance imaging (fMRI) while participants were solving visuospatial tasks. This allowed us to observe both the behavioral and the neural effects of transient parietal activity disruption in the active healthy human brain. Our results show that right, but not left, parietal TMS impairs visuospatial judgment, induces neural activity changes in a specific right-hemispheric network of frontoparietal regions, and shows significant correlations between the induced behavioral impairment and neural activity changes in both the directly stimulated parietal and remote ipsilateral frontal brain regions. The revealed right-hemispheric neural network effect of parietal TMS represents the same brain areas that are functionally connected during the execution of visuospatial judgments. This corroborates the notion that visuospatial deficits following parietal damage are brought about by a perturbation of activity across a specific frontoparietal network, rather than the lesioned parietal site alone. Our experiments furthermore show how concurrent fMRI and magnetic brain stimulation during active task execution hold the potential to identify and visualize networks of brain areas that are functionally related to specific cognitive processes.