Direct current stimulation over MT+/V5 modulates motion aftereffect in humans

While there is strong evidence for the central role of the human MT+/V5 in motion processing, its involvement in motion adaptation is still the subject of debate. We used transcranial direct current stimulation (tDCS) to test whether MT+/V5 is part of the neural network involved in the long-term adaptation-induced motion after-effect in humans. It was found that both cathodal and anodal stimulation over MT+/V5 resulted in a significant reduction of the perceived motion after-effect duration, but had no effect on performance in a luminance-change-detection task used to determine attentional load during adaptation. Our control experiment excluded the possibility that the observed MT+/V5 stimulation effects were due to a diffused modulation of the early cortical areas, i.e. by the stimulation applied over MT+/V5. These results provide evidence that external modulation of neural excitability in human MT+/V5 affects the strength of perceived motion after-effect and support the involvement of MT+/V5 in motion adaptation processes.     

Repetitive transcranial magnetic stimulation of human area MT/V5 disrupts perception and storage of the motion aftereffect

Following adaptation to a moving stimulus, the introduction of a stationary pattern creates the illusion of motion. This phenomenon, known as the motion aftereffect (MAE), can be delayed by placing a blank storage interval between the adapting and test stimuli. Human motion selective area MT/V5 has been proposed as the likely neural origin of MAEs. To examine the role of MT/V5 in perceiving and storing MAEs, we applied repetitive transcranial magnetic stimulation (rTMS) to this area during a 10 s storage interval and while subjects perceived illusory motion. Our results show that rTMS disrupts perception of the MAE when it is delivered in the early parts of the storage period and when it is applied during the perceptual MAE itself. Stimulation of control regions corresponding to V1 or Cz did not affect the MAE. In addition, magnetic stimulation of dorsolateral prefrontal and posterior parietal cortices did not disrupt MAE perception. These data provide experimental support for the notion that MT/V5 subserves perception and storage of the motion aftereffect.     

Spatial and temporal characteristics of visual motion perception involving V5 visual cortex

The anatomical substrates of the perception of motion have not yet been established in a detailed way on an individual level. The aim of this study was to develop a systematic procedure for mapping the visual cortex using Transcranial Magnetic Stimulation (TMS). The results showed that such an individual and detailed map of the spatial and temporal characteristics of motion perception can be constructed using TMS.     

Spatial and temporal characteristics of visual motion perception involving V5 visual cortex

Abstract

The anatomical substrates of the perception of motion have not yet been established in a detailed way on an individual level. The aim of this study was to develop a systematic procedure for mapping the visual cortex using Transcranial Magnetic Stimulation (TMS). The results showed that such an individual and detailed map of the spatial and temporal characteristics of motion perception can be constructed using TMS. [Neurol Res 2002; 24: 266-270]     

Magnetic stimulation over the cerebellum in humans

Magnetic stimulation performed with a double-cone coil placed over appropriate positions on the back of the head reduced the size of electromyographic responses evoked by magnetic cortical stimulation in the first dorsal interosseous muscle when it preceded the cortical stimulus by 5, 6, and 7 msec. No suppression of responses to electrical cortical stimulation occurred. Greater suppression was evoked by stronger cerebellar stimuli; lesser suppression was elicited by stronger cortical stimuli. These physiological findings correspond to those obtained with electrical cerebellar stimulation. The most effective position for magnetic stimulation over the back of the head was slightly rostral to the foramen magnum level on the ipsilateral side of the muscle studied. This indicates that the conditioning stimulus activates certain structures at the back of the head on the ipsilateral side of the muscle, consistent with the cerebellum, because the part of the cerebellum regulating limb muscles is positioned about there on the ipsilateral side. In 2 patients with only cerebellar dysfunction, this suppression effect was not elicited, which also supports that the suppression is caused by activity in cerebellar structures. We conclude that magnetic stimulation over the cerebellum with a doublecone coil elicits the same suppressive effect on the motor cortex as electrical stimulation, but with less discomfort; moreover, we believe that this effect is produced by activation of certain cerebellar structures.     

Direct current stimulation over the human sensorimotor cortex modulates the brain's hemodynamic response to tactile stimulation

Tactile stimuli produce afferent signals that activate specific regions of the cerebral cortex. Noninvasive transcranial direct current stimulation (tDCS) effectively modulates cortical excitability. We therefore hypothesised that a single session of tDCS targeting the sensory cortices would alter the cortical response to tactile stimuli. This hypothesis was tested with a block‐design functional magnetic resonance imaging protocol designed to quantify the blood oxygen level‐dependent response to controlled sinusoidal pressure stimulation applied to the right foot sole, as compared with rest, in 16 healthy young adults. Following sham tDCS, right foot sole stimulation was associated with activation bilaterally within the precentral cortex, postcentral cortex, middle and superior frontal gyri, temporal lobe (subgyral) and cingulate gyrus. Activation was also observed in the left insula, middle temporal lobe, superior parietal lobule, supramarginal gyrus and thalamus, as well as the right inferior parietal lobule and claustrum (false discovery rate corrected, P < 0.05). To explore the regional effects of tDCS, brain regions related to somatosensory processing, and cortical areas underneath each tDCS electrode, were chosen as regions of interest. Real tDCS, as compared with sham tDCS, increased the percent signal change associated with foot stimulation relative to rest in the left posterior paracentral lobule. These results indicate that tDCS acutely modulated the cortical responsiveness to controlled foot pressure stimuli in healthy adults. Further study is warranted, in both healthy individuals and patients with sensory impairments, to link tDCS‐induced modulation of the cortical response to tactile stimuli with changes in somatosensory perception.     

Pain perception in humans: use of intraepidermal electrical stimulation

The choice of a system specific stimulus is difficult when investigating the human nociceptive system, in contrast with the tactile, auditory and visual systems, because it should be noxious but not actually damage the tissue. The discomfort accompanying system specific stimulation must be kept to a minimum for ethical reasons. In this review, recent progress made in the study of human pain perception using intraepidermal electrical stimulation (IES) is described. Also, whether IES is a viable alternative to laser stimulation is discussed. IES selectively activates Aδ nociceptors, elicits a sharp pricking sensation with minimal discomfort and evokes cortical responses almost identical to those produced by laser stimulation. As IES does not require expensive equipment, and is easy to control, it would seem useful for pain research as well as clinical tests.     

Physiology of perception: cortical stimulation and recording in humans

OBJECTIVES: 1) To determine the effect of stimulus train duration (TD) on sensory perception using direct stimulation of somatosensory and visual cortices. 2) To investigate the occurrence of evoked potentials in response to stimulation that is subthreshold for perception. BACKGROUND: Studies of the mechanisms of conscious perception using direct cortical stimulation and recording techniques are rare. The clinical necessity to implant subdural electrode grids in epilepsy patients undergoing evaluation for surgery offers an opportunity to examine the role of stimulus parameters and evoked potentials in conscious perception. METHODS: Subjects included epilepsy patients with grids over somatosensory or occipital cortex. Single pulses (100 microseconds) and stimulus trains were applied to electrodes, and thresholds for perception were found. Evoked potentials were recorded in response to peripheral stimulation at intensities at, above, and below sensory threshold. RESULTS: During cortical stimulation, sensory threshold changed little for stimulus trains of 250 milliseconds and longer, but increased sharply as TD decreased below this level. Primary evoked activity was recorded in response to peripheral stimulations that were subthreshold for conscious perception. CONCLUSIONS: The results confirm a previous report of the effects of stimulus TD on sensory threshold. However, no motor responses occurred following somatosensory stimulation with short trains, as previously reported. The TD threshold pattern was similar in visual cortex. In agreement with the previous report, early components of the primary evoked response were not correlated with conscious sensory awareness.     

Post training REMs coincident auditory stimulation enhances memory in humans

Sleep activity was monitored in 20 freshman college students for two consecutive nights. Subjects were assigned to 4 equal groups and all were asked to learn a complex logic task before bed on the second night. Two groups of subjects learned the task with a constant clicking noise in the background (cued groups), while two groups simply learned the task (non cued). During the night, one cued and one non cued group were presented with auditory clicks during REM sleep such as to coincide with all REMs of at least 100 microvolts. The second cued group was given auditory clicks during REM sleep, but only during the REMs "quiet" times. The second non-cued control group was never given any nighttime auditory stimulations. The cued REMs coincident group showed a significant 23% improvement in task performance when tested one week later. The non cued REMs coincident group showed only an 8.8% improvement which was not significant. The cued REMs quiet and non-stimulated control groups showed no change in task performance when retested. The results were interpreted as support for the idea that the cued auditory stimulation induced a "recall" of the learned material during the REM sleep state in order for further memory processing to take place.     

Disruptions to human speed perception induced by motion adaptation and transcranial magnetic stimulation

To investigate the underlying nature of the effects of transcranial magnetic stimulation (TMS) on speed perception, we applied repetitive TMS (rTMS) to human V5/MT+ following adaptation to either fast‐ (20 deg/s) or slow (4 deg/s)‐moving grating stimuli. The adapting stimuli induced changes in the perceived speed of a standard reference stimulus moving at 10 deg/s. In the absence of rTMS, adaptation to the slower stimulus led to an increase in perceived speed of the reference, whilst adaptation to the faster stimulus produced a reduction in perceived speed. These induced changes in speed perception can be modelled by a ratio‐taking operation of the outputs of two temporally tuned mechanisms that decay exponentially over time. When rTMS was applied to V5/MT+ following adaptation, the perceived speed of the reference stimulus was reduced, irrespective of whether adaptation had been to the faster‐ or slower‐moving stimulus. The fact that rTMS after adaptation always reduces perceived speed, independent of which temporal mechanism has undergone adaptation, suggests that rTMS does not selectively facilitate activity of adapted neurons but instead leads to suppression of neural function. The results highlight the fact that potentially different effects are generated by TMS on adapted neuronal populations depending upon whether or not they are responding to visual stimuli.     

Anodal transcranial direct current stimulation over the right dorsolateral prefrontal cortex enhances reflective judgment and decision-making

Background

Accounts of cognitive processes in judgment and decision-making are frequently based on a dual-process framework, which reflects two qualitatively different types of processing: intuitive (Type 1) and analytical (Type 2) processes.

Oscillatory brain activity and transcranial direct current stimulation in humans

The aim of this study was to induce changes of the oscillatory activity in the visual cortex of healthy human subjects by modulation of neuronal excitability using weak transcranial direct current stimulation (tDCS). tDCS is a non-invasive stimulation method which induces prolonged, polarity-dependent increases or reductions in cortical excitability. An increase in high frequency oscillatory activity in the beta and gamma frequency ranges is closely related in time to the N70 peak of the primary visual evoked potential (VEP), which is an early sensory component of visual activation. Therefore this potential can be used to observe tDCS-induced changes related to oscillatory activity. VEPs were recorded using sinusoidal luminance gratings in an on/off mode before, immediately after and 10, 20, 30 min after the end of 10 min anodal or cathodal stimulation. Cathodal stimulation significantly decreased while anodal stimulation slightly increased the normalized beta and gamma frequency powers. We have shown here that tDCS transiently and reversibly changed the organized cortical activity elicited by visual stimulation. Since gamma activity is also related to a higher level of information processing, tDCS might be a suitable method to affect higher order cognitive processes.     

Anodal transcranial direct current stimulation (tDCS) over supplementary motor area (SMA) but not pre-SMA promotes short-term visuomotor learning

BackgroundNon-invasive brain stimulation such as transcranial direct current stimulation (tDCS) has been shown to modulate cortical excitability and thereby influencing motor behaviour and learning.HypothesisWhile there is increasing knowledge about the importance of the primary motor cortex (M1) in short- and long-term motor skill learning, little is known about the role of secondary motor areas such as the supplementary and pre-supplementary motor area (SMA/pre-SMA) especially in short-term motor performance. Since SMA but not pre-SMA is directly connected to M1, we hypothesize that anodal tDCS over SMA but not pre-SMA will facilitate visuomotor learning.MethodsWe applied anodal tDCS (tDCS_anodal) over left SMA, pre-SMA or M1 (n = 12 in each group) while subjects performed a visuomotor pinch force task (VPFT) with their right hand and compared VPFT performance relative to sham (tDCS_sham).ResultsFor the first time, we could show that apart from tDCS_anodal over left M1 also SMA but not pre-SMA stimulation promotes short-term improvements in visuomotor learning relative to tDCS_sham.ConclusionsOur findings provide novel evidence about the role of SMA in short-term visuomotor performance. This knowledge might be beneficial in developing hypothesis-driven clinical studies in neurorehabilitation.     

The role of MT+/V5 during biological motion perception in Asperger Syndrome: An fMRI study

Asperger Syndrome (AS), a condition on the autistic spectrum, is characterized by deficits in the ability to use social cues to infer mental state information. Few studies have examined whether these deficits might be understood in terms of differences in visual information processing. The present study employed functional magnetic resonance imaging to examine differences in brain activity among individuals with AS while performing a task that typically leads to the automatic interpretation of human movement. Despite similar behavioural performance, significantly less activity was found for the AS group (relative to a control group) in inferior, middle and superior temporal regions, including the human analogue of MT+/V5. These data suggest that AS is associated with unique patterns of brain activity during the perception of visually presented social cues.     

Transcutaneous spinal direct current stimulation improves locomotor learning in healthy humans

Background

Ambulation is an essential aspect of daily living and is often impaired after brain and spinal cord injuries. Despite the implementation of standard neurorehabilitative care, locomotor recovery is often incomplete.