Perturbation of visuospatial attention by high-frequency offline rTMS

The contribution of different cortical regions to visuospatial attention can be probed with the help of perturbation techniques, such as transcranial magnetic stimulation (TMS). Repetitive TMS (rTMS) has also been suggested as a tool for the therapy of brain injuries, by adjusting the neural excitability of injured or intact brain regions. Low- and high-frequency rTMS have been shown to result in subsequent (offline) reductions or increases of local cortical excitability, respectively. Previous studies demonstrated that low-frequency (1 Hz) rTMS of posterior parietal cortex (PPC) produced significantly reduced detection of stimuli in the visual hemifield contralateral to the stimulation site, as well as increased ipsilateral detection. We here explored the functional impact of high-frequency (20 Hz) rTMS with an attention task similar to that of a previous low-frequency study (Hilgetag et al. in Nat Neurosci 4:953–957, 2001). Normal healthy subjects (N = 14) received high-frequency rTMS (20 Hz, 10 min, 50% stimulator output) over right or left PPC (coordinate points P4 or P3). After stimulation of the right PPC, detection of single visual stimuli in the contralateral hemifield was significantly impaired. Generally, rTMS of right and left PPC produced mirror-symmetric trends in reduced contralateral detection. These effects were still present after post-TMS sham stimulation (more than 20 min after the end of active rTMS). The results suggest that attentional function can be perturbed by high-frequency rTMS as well as by low-frequency rTMS, despite potential differences in the underlying neural mechanisms. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Interaction between finger opposition movements and aftereffects of 1Hz-rTMS on ipsilateral motor cortex

One-hertz repetitive transcranial magnetic stimulation (1Hz-rTMS) over ipsilateral motor cortex is able to modify up to 30 min the motor performance of repetitive finger opposition movements paced with a metronome at 2 Hz. We investigated whether the long-lasting rTMS effect on motor behavior can be modulated by subsequent engagement of the contralateral sensorimotor system. Motor task was performed in different experimental conditions: immediately after rTMS, 30 min after rTMS, or when real rTMS was substituted with sham rTMS. Subjects performing the motor task immediately after rTMS showed modifications in motor behavior < or =30 min after rTMS. On the other hand, when real rTMS was substituted with sham stimulation or when subjects performed the motor task 30 min after the rTMS session, the effect was no longer present. These findings suggest that the combination of ipsilateral 1Hz-rTMS and voluntary movement is crucial to endure the effect of rTMS on the movement itself, probably acting on synaptic plasticity-like mechanism. This finding might provide some useful hints for neurorehabilitation protocols.     

Cathodal transcranial direct current stimulation on posterior parietal cortex disrupts visuo-spatial processing in the contralateral visual field

Transcranial direct current stimulation (tDCS) has recently undergone a resurgence in popularity as a powerful tool to non-invasively manipulate brain activity. While tDCS has been used to alter functions tied to primary motor and visual cortices, its impact on extrastriate visual areas involved in visuo-spatial processing has not yet been examined. In the current study, we applied tDCS to the cat visuoparietal (VP) cortex and assayed performance in a paradigm designed to assess the capacity to detect, localize and orient to static targets appearing at different spatial eccentricities within the visual field. Real or sham cathodal tDCS was unilaterally applied to the VP cortex, and orienting performance was assessed during (online), immediately after (offline; Experiments 1 and 2), and 1 or 24 h after the end of the tDCS stimulation (Experiment 2). Performance was compared to baseline data collected immediately prior to stimulation. Real, but not sham, tDCS induced significant decreases in performance for static visual targets presented in the contrastimulated visual hemifield. The behavioral impact of tDCS was most apparent during the online and immediate offline periods. The tDCS effect decayed progressively over time and performance returned to baseline levels ∼60 min after stimulation. These results are consistent with the effects of both invasive and non-invasive deactivation methods applied to the same brain region, and indicate that tDCS has the potential to modify neuronal activity in extrastriate visual regions and to sculpt brain activity and behavior in normal and neurologically impaired subjects. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Contributions of human parietal and frontal cortices to attentional control during conflict resolution: a 1-Hz offline rTMS study

Various brain regions contribute to aspects of attentional control in conflict resolution. Here, we used transcranial magnetic stimulation (TMS) to examine the functions of posterior parietal cortex (PPC) and dorsal medial frontal cortex (dMFC) in a visual flanker task. Participants responded to a central target that was flanked by congruent, neutral or incongruent stimuli on the left or right. Offline low-frequency repetitive TMS (1 Hz, 110% motor threshold, 20 min) was applied to right PPC or dMFC. Performance, as measured by reaction times and accuracy, was established at baseline, after rTMS, and sham stimulation before or after active rTMS. After rTMS to right PPC, the interference of flankers presented in the left visual hemispace diminished selectively. By contrast, after rTMS over the right dMFC, flanker effects in both visual fields remained. Our results suggest that right PPC specifically contributes to the assignment of spatial attention during stimulus encoding.     

Changes of blood lactate levels after repetitive transcranial magnetic stimulation

The objective was to study whether repetitive transcranial magnetic stimulation (rTMS) of the motor cortex could induce modification of peripheral blood lactate values. Nineteen young healthy volunteers were included; during the study, all subjects were at rest, sitting on a comfortable armchair. The muscular activation was evaluated by continuous electromyographic record. TMS was performed by using a circular coil at the vertex. Resting motor threshold (rMT) was defined as the lowest TMS intensity able to induce motor responses of an amplitude >50 μV in the relaxed contralateral target muscle in approximately 50% of 20 consecutive stimuli. Venous blood lactate values were measured before, immediately after and 10 min after a single session of low frequencies (1 Hz for 15 min) rTMS (LF rTMS) or high frequency (20 Hz for 15 min) rTMS (HF rTMS). As expected, LF rTMS induced a decrease of motor cortex excitability, whereas HF rTMS evoked an increase of motor cortex excitability. However, in the present investigation we observed that both conditions are associated to a significant increase of blood lactate. Since in our experimental conditions we can exclude a muscular production of lactate, the significant increment of peripheral blood lactate values, observed 10 min after the end of the rTMS session, is probably due to the crossing by brain-produced lactate of the blood–brain barrier.     

A comparison of the effects of bilateral and unilateral infusions of muscimol into the basal forebrain on cued detection of visual targets in rats

This study investigated the role of the basal forebrain cholinergic system (BFCS) in rats' performance of a visuospatial attention task. Muscimol was infused bilaterally and unilaterally into the BFCS to inhibit cholinergic projections to the cortex. Muscimol slowed responding without significantly affecting side-bias. Bilateral infusions increased accuracy for all targets, whereas unilateral infusions reduced accuracy for targets contralateral to the infusion and increased accuracy for targets ipsilateral to the infusion. After a low unilateral dose of muscimol, invalid cues impaired detection of contralateral targets and spared detection of ipsilateral targets. A high unilateral dose of muscimol impaired detection of contralateral targets independently of cueing. These results suggest that interhemispheric imbalance in cortical activity by pharmacological manipulation of the BFCS can impair the detection of lateralized visual stimuli.     

Enhanced visual spatial attention ipsilateral to rTMS-induced 'virtual lesions' of human parietal cortex

The breakdown of attentional mechanisms after brain damage can have drastic behavioral consequences, as in patients suffering from spatial neglect. While much research has concentrated on impaired attention to targets contralateral to sites of brain damage, here we report the ipsilateral enhancement of visual attention after repetitive transcranial magnetic stimulation (rTMS) of parietal cortex at parameters known to reduce cortical excitability. Normal healthy subjects received rTMS (1 Hz, 10 mins) over right or left parietal cortex. Subsequently, detection of visual stimuli contralateral to the stimulated hemisphere was consistently impaired when stimuli were also present in the opposite hemifield, mirroring the extinction phenomenon commonly observed in neglect patients. Additionally, subjects' attention to ipsilateral targets improved significantly over normal levels. These results underline the potential of focal brain dysfunction to produce behavioral improvement and give experimental support to models of interhemispheric competition in the distributed brain network for spatial attention.     

Cortical control of sound localization in the cat: unilateral cooling deactivation of 19 cerebral areas

We examined the ability of mature cats to accurately orient to, and approach, an acoustic stimulus during unilateral reversible cooling deactivation of primary auditory cortex (AI) or 1 of 18 other cerebral loci. After attending to a central visual stimulus, the cats learned to orient to a 100-ms broad-band, white-noise stimulus emitted from a central speaker or 1 of 12 peripheral sites (at 15 degrees intervals) positioned along the horizontal plane. Twenty-eight cats had two to six cryoloops implanted over multiple cerebral loci. Within auditory cortex, unilateral deactivation of AI, the posterior auditory field (PAF) or the anterior ectosylvian sulcus (AES) resulted in orienting deficits throughout the contralateral field. However, unilateral deactivation of the anterior auditory field, the second auditory cortex, or the ventroposterior auditory field resulted in no deficits on the orienting task. In multisensory cortex, unilateral deactivation of neither ventral or dorsal posterior ectosylvian cortices nor anterior or posterior area 7 resulted in any deficits. No deficits were identified during unilateral cooling of the five visual regions flanking auditory or multisensory cortices: posterior or anterior ii suprasylvian sulcus, posterior suprasylvian sulcus or dorsal or ventral posterior suprasylvian gyrus. In motor cortex, we identified contralateral orienting deficits during unilateral cooling of lateral area 5 (5L) or medial area 6 (6m) but not medial area 5 or lateral area 6. In a control visual-orienting task, areas 5L and 6m also yielded deficits to visual stimuli presented in the contralateral field. Thus the sound-localization deficits identified during unilateral deactivation of area 5L or 6m were not unimodal and are most likely the result of motor rather than perceptual impairments. Overall, three regions in auditory cortex (AI, PAF, AES) are critical for accurate sound localization as assessed by orienting.     

The left visual-field advantage in rapid visual presentation is amplified rather than reduced by posterior-parietal rTMS

In the present task, series of visual stimuli are rapidly presented left and right, containing two target stimuli, T1 and T2. In previous studies, T2 was better identified in the left than in the right visual field. This advantage of the left visual field might reflect dominance exerted by the right over the left hemisphere. If so, then repetitive transcranial magnetic stimulation (rTMS) to the right parietal cortex might release the left hemisphere from right-hemispheric control, thereby improving T2 identification in the right visual field. Alternatively or additionally, the asymmetry in T2 identification might reflect capacity limitations of the left hemisphere, which might be aggravated by rTMS to the left parietal cortex. Therefore, rTMS pulses were applied during each trial, beginning simultaneously with T1 presentation. rTMS was directed either to P4 or to P3 (right or left parietal cortex) either as effective or as sham stimulation. In two experiments, either one of these two factors, hemisphere and effectiveness of rTMS, was varied within or between participants. Again, T2 was much better identified in the left than in the right visual field. This advantage of the left visual field was indeed modified by rTMS, being further increased by rTMS to the left hemisphere rather than being reduced by rTMS to the right. It may be concluded that superiority of the right hemisphere in this task implies that this hemisphere is less irritable by external interference than the left hemisphere.     

Neuroplasticity in the cat’s visual system: test of the role of the expanded retino-geniculo-parietal pathway in behavioral sparing following early lesions of visual cortex

Sparing of the ability to redirect head and eyes to new stimuli and expansion of the retino-geniculo-parietal pathway are both robust aspects of the repercussions of early lesions of occipital visual areas in cats. The purpose of the present work was to test the proposition that the pathway expansions and spared behaviors are causally linked. The proposition was tested by deactivating either the dorsal lateral geniculate nucleus (dLGN) and thereby uncoupling the primary and secondary limbs of the retino-geniculo-parietal pathway, or silencing the terminus of the pathway, and then testing the ability of cats to detect and orient head and eyes to visual targets. Six cats sustained experimental unilateral lesions of occipital areas 17 and 18 and variable amounts of area 19 on postnatal days 1-2 or 26-30 to induce rewiring and expansion of visual pathways from retina through the dLGN onto a critical region of visuoparietal (VP) cortex. Unilateral lesions ensured that we could use the orienting performance of the intact hemisphere as a fiduciary marker of performance against which performance of the experimental hemisphere could be gauged. When the cats were adult, a secondary test lesion was made on the damaged side by injecting, under electrophysiological guidance, ibotenic acid into either dLGN of four cats or into VP cortex of two cats. Prior to injection of ibotenic acid, all cats oriented head and eyes with high proficiency throughout the contralesional field, and performance was indistinguishable from orienting to stimuli presented in the ipsilesional field; sparing of the orienting behavior was complete. Ibotenic acid lesions of both dLGN and VP cortex induced a profound neglect of stimuli introduced into the contralesional hemifield. Orienting into the ipsilesional field remained high throughout. Subsequently, there was restoration of orienting behavior over the next 4-6 (dLGN deactivation) and 9-12 (VP deactivation) days. The test results demonstrate the essential contribution made by the retino-geniculo-parietal pathway to the ability to detect and redirect head and eyes to look at visual stimuli following early lesions of occipital visual cortices. The subsequent post-test lesion restoration of high orienting proficiency shows that in the absence of dLGN, or the critical region of VP cortex, other regions of cerebral cortex, or other structures such as the superior colliculus, can emerge and make important contributions to orienting behavior. These results reveal a maintained residual, beneficial adaptive plasticity of mature neural circuits even in brains compromised by early lesions of occipital visual areas.     

Magnetic stimulation and the crossed–uncrossed difference (CUD) paradigm: selective effects in the ipsilateral and contralateral hemispheres

When a visual target is presented to one hemifield, manual responses made to the target using the ipsilateral hand (uncrossed responses) are faster than responses using the contralateral hand (crossed response), because there is no need for visuomotor information to be transferred between the hemispheres. This difference in response times is termed the crossed–uncrossed difference (CUD) and is a valuable means of estimating interhemispheric transfer time. We aimed to investigate the CUD by applying repetitive transcranial magnetic stimulation (rTMS) over the left and right occipital cortex during a lateralized target-detection task. Eleven neurologically healthy subjects, all right-handed, participated in the study. Relative to sham TMS we increased the CUD, by inhibiting the crossed latencies, but only when rTMS was applied to the hemisphere receiving visual information. These results replicate and extend previous findings and suggest the inhibitory rTMS effect under the crossed condition might be because the weak visual output is unable to activate the crossed pathway.     

Electrophysiological correlates of visually processing subject's own name

The study aimed to test the modulation induced by 1 Hz repetitive Transcranial Magnetic Stimulation (rTMS) of the occipital cortex on the alpha phase synchronization under repetitive flash stimuli in 15 migraine without aura patients compared to 10 controls. The EEG was recorded by 7 channels, while flash stimuli were delivered at 9, 18, 21 and 24 Hz in basal, rTMS (15 min of 1 Hz stimulation of the occipital cortex) and sham conditions. Migraine patients displayed increased alpha-band phase synchronization under visual stimulation, while an overall desynchronizing effect was evident in controls. The rTMS resulted in a slight increase of synchronization index in migraine patients, which did not cause significant differences in respect to the basal and sham conditions. The synchronizing-desynchronizing changes of alpha rhythm under repetitive flash stimulation, seem independent from the state of occipital cortex excitability. Other mechanisms beyond cortical excitability may contribute to explain migraine pathogenesis.     

Restoration of acoustic orienting into a cortically deaf hemifield by reversible deactivation of the contralesional superior colliculus: the acoustic "Sprague Effect"

Removal of all contiguous visual cortical areas of one hemisphere results in a contralateral hemianopia. Subsequent deactivation of the contralesional superior colliculus (SC) nullifies the effects of the visual cortex ablation and restores visual orienting responses into the cortically blind hemifield. This deficit nullification has become known as the "Sprague Effect." Similarly, in the auditory system, unilateral ablation of auditory cortex results in severe sound localization deficits, as assessed by acoustic orienting, to stimuli in the contralateral hemifield. The purpose of this study was to examine whether auditory orienting responses can be restored into the impaired hemifield during deactivation of the contralesional SC. Three mature cats were trained to orient toward and approach an acoustic stimulus (broadband, white noise burst) that was presented centrally, or at one of 12 peripheral loci, spaced at 15 degrees intervals. After training, a cryoloop was chronically implanted over the dorsal surface of the right SC. During cooling of the cooling loop to temperatures sufficient to deactivate the superficial and intermediate layers (SZ, SGS, SO, SGI), auditory orienting responses were eliminated into the left (contracooled) hemifield while leaving acoustic orienting into the right (ipsicooled) hemifield unimpaired. This deficit was temperature-dependently graded from periphery to center. After the effectiveness of the SC cooling loop was verified, auditory cortex of the middle and posterior ectosylvian and anterior and posterior sylvian gyri was removed from the left hemisphere. As expected, the auditory cortex ablation resulted in a profound deficit in orienting to acoustic stimuli presented at any position in the right (contralesional) hemifield, while leaving acoustic orienting into the left (ipsilesional) hemifield unimpaired. The ablations of auditory cortex did not have any impact on a visual detection and orienting task. The additional deactivation of the contralesional SC to temperatures sufficient to cool the superficial and intermediate layers nullified the deficit caused by the auditory cortex ablation and acoustic orienting responses were restored into the right hemifield. This restoration was temperature-dependently graded from center to periphery. The deactivations were localized and confirmed with reduced uptake of radiolabeled 2-deoxyglucose. Therefore deactivation of the right superior colliculus after the ablation of the left auditory cortex yields a fundamentally different result from that identified during deactivation of the right superior colliculus before the removal of left auditory cortex in the same animal. Thus the "Sprague Effect" is not unique to a particular sensory system and deactivation of the contralesional SC can restore either visual or acoustic orienting responses into an impaired hemifield after cortical damage.     

Recovery of function following unilateral damage to visuoparietal cortex

Damage to the visuoparietal cortex located in the banks of the middle suprasylvian gyrus of the cat has been shown to produce a deficit in the detection and localization of moving visual cues presented in the contralesional visual hemifield. There is evidence from reversible cooling deactivation studies that the integrity of this orienting function is not completely dependent on the VP cortex and that under the right circumstances, other brain regions may come online and completely take over the processing that subserves this behavior. We examined the recovery of orienting behavior after unilateral damage to the VP cortex. We found that consistent with previous data, VP damage produced an impairment in the capacity to detect and orient to moving visual stimuli in the contralesional visual field. Over a span of days, spontaneous recovery fully occurred. The ability to detect and localize static visual stimuli was tested as a fiducial measure of parietal cortex function, and this function did not recover. We conclude that the detection and localization of moving visual stimuli is not a function that requires VP cortex and argue for the existence of a parallel and redundant subcortical-cortical brain network that serves as the substrate for recovery of function.     

A functional magnetic resonance imaging navigated repetitive transcranial magnetic stimulation study of the posterior parietal cortex in normal pain and hyperalgesia

Noxious stimuli activate a complex cerebral network. During central sensitization to pain, activity in most of these areas is changed. One of these areas is the posterior parietal cortex (PPC). The role of the PPC during processing of acute pain as well as hyperalgesia and tactile allodynia remains elusive. Therefore, we performed a functional magnetic resonance imaging (fMRI) based, neuro-navigated, repetitive transcranial magnetic stimulation (rTMS) study in 10 healthy volunteers. Firstly, pin-prick hyperalgesia was provoked on the right volar forearm, using the model of electrically-induced secondary mechanical hyperalgesia. fMRI was performed during pin-prick stimulation inside and outside the hyperalgesic areas. Secondly, on four different experimental sessions, the left and right individual intraparietal BOLD peak-activations were used as targets for a sham-controlled 1 Hz rTMS paradigm of 10 min duration. We measured psychophysically the (i) electrical pain stimulus intensity on an 11-point numeric pain rating scale (NRS, 0–10), the (ii) area of hyperalgesia, and the (iii) area of dynamic mechanical allodynia. Sham stimulation or rTMS was performed 16 min after induction of pin-prick hyperalgesia and tactile allodynia. Compared to sham stimulation, no significant effect of rTMS was observed on pain stimulus intensity and the area of allodynia. However, a reduction of the hyperalgesic area was observed for rTMS of the left PPC (P<0.05). We discuss the role of the PPC in central sensitization to pain, in spatial discrimination of pain stimuli and in spatial-attention to pain stimuli.     

Opposite impact on <Superscript>14</Superscript>C-2-deoxyglucose brain metabolism following patterns of high and low frequency repetitive transcranial magnetic stimulation in the posterior parietal cortex

Repetitive transcranial magnetic stimulation (rTMS) appears capable of modulating human cortical excitability beyond the duration of the stimulation train. However, the basis and extent of this “off-line” modulation remains unknown. In a group of anesthetized cats, we applied patterns of real or sham focal rTMS to the visuo-parietal cortex (VP) at high (HF) or low (LF) frequency and recorded brain glucose uptake during (on-line), immediately after (off-line), or 1 h after (late) stimulation. During the on-line period LF and HF rTMS induced a significant relative reduction of ¹⁴C-2DG uptake in the stimulated VP cortex and tightly linked cortical and subcortical structures (e.g. the superficial superior colliculus, the pulvinar, and the LPl nucleus) with respect to homologue areas in the unstimulated hemisphere. During the off-line period HF rTMS induced a significant relative increase in ¹⁴C-2DG uptake in the targeted VP cortex, whereas LF rTMS generated the opposite effect, with only mild network impact. Moderate distributed effects were only recorded after LF rTMS in the posterior thalamic structures. No long lasting cortical or subcortical effects were detected during the late period. Our findings demonstrate opposite modulation of rTMS on local and distant effects along a specific network, depending on the pattern of stimulation. Such effects are demonstrated in the anesthetized animal, ruling out behavioral and non-specific reasons for the differential impact of the stimulation. The findings are consistent with previous differential electrophysiological and behavioral effects of low and high frequency rTMS patterns and provide support to uses of rTMS in neuromodulation. ^†Prof. Payne passed away in May 2004. This article is submitted in his memory.     

Role of the cerebellum in externally paced rhythmic finger movements

Several studies have suggested that the cerebellum has an important role in timing of subsecond intervals. Previous studies using transcranial magnetic stimulation (TMS) to test this hypothesis directly have produced inconsistent results. Here we used 1-Hz repetitive TMS (rTMS) for 10 min over the right or left cerebellar hemisphere to interfere transiently with cerebellar processing to assess its effect on the performance of a finger-tapping task. Subjects tapped with their right index finger for 1 min (synchronization phase) with an auditory or visual cue at 0.5, 1, or 2 Hz; they continued for a further 1 min at the same rate with no cues (continuation phase). The blocks of trials were performed in a random order. rTMS of the cerebellum ipsilateral to the movement increased the variability of the intertap interval but only for movements at 2 Hz that were made while subjects were synchronizing with an auditory cue. There was no effect on the continuation phase of the task when the cues were no longer present or on synchronization with a visual cue. Similar results were seen after stimulation over the contralateral dorsal premotor cortex but not after rTMS over supplementary motor area. There was no effect after rTMS over the ipsilateral right cervical nerve roots or over the ipsilateral primary motor cortex. The results support the hypothesis of neural network for event-related timing in the subsecond range that involves a cerebellar-premotor network.     

The role of human extra-striate visual areas V5/MT and V2/V3 in the perception of the direction of global motion: a transcranial magnetic stimulation study

Several published single case studies reveal a double dissociation between the effects of brain damage in separate extra-striate cortical visual areas on the perception of global visual motion defined by a difference in luminance (first-order motion) versus motion defined by a difference in contrast (second-order motion). In particular, the medial extrastriate cortical region V2/V3 seems to be crucial for the perception of first-order motion, but not for second-order, whereas a lateral and more anterior portion of the cortex close to the temporo–parieto–occipital junction (in the territory of the human motion area hV5/MT⁺) seems to be essential only for the perception of second-order motion. In order to test the hypothesis of a functional specialization of different visual areas for different types of motion, we applied repetitive transcranial magnetic stimulation (rTMS) unilaterally over areas V2/V3, V5/MT, or posterior parietal cortex (PPC) while subjects performed a 2AFC task with first- or second-order global motion displays in the contralateral visual field. Results showed a comparable disruption of the two types of motion, with both rTMS over V2/V3 or over MT/V5, and little or no effect with rTMS over PPC. The results suggest that either the previous psychophysical results with neurological patients are incorrect (highly unlikely) or that the lateral and medial regions are directly connected (as they are in macaque monkeys) such that stimulating one automatically affects the other, in this instance disruptively     

Substance P immunoreactive nerve fibres in the domestic chick ankle joint before and after acute urate arthritis

In complex regional pain syndrome (CRPS) many clinical symptoms suggest involvement of the central nervous system. Neuropathic pain as the leading symptom is often resistant to therapy. In the present study we investigated the analgesic efficiency of repetitive transcranial magnetic simulation (rTMS) applied to the motor cortex contralateral to the CRPS-affected side. Seven out of ten patients reported decreased pain intensities. Pain relief occurred 30 s after stimulation, whereas the maximum effect was found 15 min later. Pain re-intensified increasingly 45 min after rTMS. In contrast, sham rTMS did not alter pain perception. These findings provide evidence that in CRPS I pain perception can be modulated by repetitive motor cortex stimulation.     

Restoration of visual orienting into a cortically blind hemifield by reversible deactivation of posterior parietal cortex or the superior colliculus

A contralateral hemineglect of the visual field can be induced by unilateral cooling deactivation of posterior middle suprasylvian (pMS) sulcal cortex of the posterior parietal region, and this neglect can be reversed by additional cooling deactivation of pMS cortex in the opposite hemisphere. The purpose of the present study was to test whether an enduring hemianopia induced by removal of all contiguous visual cortical areas of one hemisphere could be reversed by local cooling of pMS cortex in the opposite hemisphere. Two cats sustained large unilateral ablations of the contiguous visual areas, and cooling loops were placed in the pMS sulcus, and in contact with adjacent area 7 or posterior ectosylvian (PE) cortex of the opposite hemisphere. In both instances cooling of pMS cortex, but neither area 7 nor PE, restored a virtually normal level of orienting performance to stimuli presented anywhere in the previously hemianopic field. The reversal was highly sensitive to the extent of cooling deactivation. In a third cat, cooling deactivation of the superficial layers of the contralateral superior colliculus also restored orienting performance to a cortical ablation-induced hemianopia. This reversal was graded from center-to-periphery in a temperature-dependent manner. Neither the cortical ablation nor any of the cooling deactivations had any impact on an auditory detection and orienting task. The deactivations were localized and confirmed by reduced uptake of radiolabeled 2-deoxyglucose to be limited to the immediate vicinity of each cooling loop. The results are discussed in terms of excitation and disinhibition of visual circuits.