Magnetoencephalographic study of event‐related fields and cortical oscillatory changes during cutaneous warmth processing

Thermoreception is an important cutaneous sense, which plays a role in the maintenance of our body temperature and in the detection of potential noxious heat stimulation. In this study, we investigated event‐related fields (ERFs) and neural oscillatory activities, which were modulated by warmth stimulation. We developed a warmth stimulator that could elicit a warmth sensation, without pain or tactile sensation, by using a deep‐penetrating 980‐nm diode laser. The index finger of each participant (n = 24) was irradiated with the laser warmth stimulus, and the cortical responses were measured using magnetoencephalography (MEG). The ERFs and oscillatory responses had late latencies (～1.3 s and 1.0–1.5 s for ERFs and oscillatory responses, respectively), which could be explained by a slow conduction velocity of warmth‐specific C‐fibers. Cortical sources of warmth‐related ERFs were seen in the bilateral primary and secondary somatosensory cortices (SI and SII), posterior part of the anterior cingulate cortex (pACC), ipsilateral primary motor, and premotor cortex. Thus, we suggested that SI, SII, and pACC play a role in processing the warmth sensation. Time–frequency analysis demonstrated the suppression of the alpha (8–13 Hz) and beta (18–23 Hz) band power in the bilateral sensorimotor cortex. We proposed that the suppressions in alpha and beta band power are involved in the automatic response to the input of warmth stimulation and sensorimotor interactions. The delta band power (1–4 Hz) increased in the frontal, temporal, and cingulate cortices. The power changes in delta band might be related with the attentional processes during the warmth stimulation.     

Neuronal network pharmacodynamics of GABAergic modulation in the human cortex determined using pharmaco‐magnetoencephalography

Neuronal network oscillations are a unifying phenomenon in neuroscience research, with comparable measurements across scales and species. Cortical oscillations are of central importance in the characterization of neuronal network function in health and disease and are influential in effective drug development. Whilst animal in vitro and in vivo electrophysiology is able to characterize pharmacologically induced modulations in neuronal activity, present human counterparts have spatial and temporal limitations. Consequently, the potential applications for a human equivalent are extensive. Here, we demonstrate a novel implementation of contemporary neuroimaging methods called pharmaco‐magnetoencephalography. This approach determines the spatial profile of neuronal network oscillatory power change across the cortex following drug administration and reconstructs the time course of these modulations at focal regions of interest. As a proof of concept, we characterize the nonspecific GABAergic modulator diazepam, which has a broad range of therapeutic applications. We demonstrate that diazepam variously modulates θ (4–7 Hz), α (7–14 Hz), β (15–25 Hz), and γ (30–80 Hz) frequency oscillations in specific regions of the cortex, with a pharmacodynamic profile consistent with that of drug uptake. We examine the relevance of these results with regard to the spatial and temporal observations from other modalities and the various therapeutic consequences of diazepam and discuss the potential applications of such an approach in terms of drug development and translational neuroscience. Hum Brain Mapp, 2010. © 2009 Wiley‐Liss, Inc.     

Functional integrity of thalamocortical circuits differentiates normal aging from mild cognitive impairment

Resonance in thalamocortical networks is critically involved in sculpting oscillatory behavior in large ensembles of neocortical cells. Neocortical oscillations provide critical information about the integrity of thalamocortical circuits and functional connectivity of cortical networks, which seem to be significantly disrupted by the neuronal death and synapse loss characterizing Alzheimer's disease (AD). By applying a novel analysis methodology to overcome volume conduction effects between scalp electroencephalographic (EEG) measurements, we were able to estimate the temporal activation of EEG‐alpha sources in the thalamus and parieto‐occipital regions of the cortex. We found that synaptic flow underlying the lower alpha band (7.5–10 Hz) was abnormally facilitated in patients with mild cognitive impairment (MCI) as compared to healthy elderly individuals, particularly from thalamus to cortex (～38% higher). In addition, the thalamic generator of lower alpha oscillations was also abnormally activated in patients with MCI. Regarding the upper alpha subdivision (10.1–12.5 Hz), both controls and patients with MCI showed a bidirectional decrease of thalamocortical synaptic transmission, which was age‐dependent only in the control group. Altogether, our results suggest that functional dynamics of thalamocortical networks differentiate individuals at high risk of developing AD from healthy elderly subjects, supporting the hypothesis that neurodegeneration mechanisms are active years before the patient is clinically diagnosed with dementia. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.     

Whole‐brain structural connectivity in dyskinetic cerebral palsy and its association with motor and cognitive function

Dyskinetic cerebral palsy (CP) has long been associated with basal ganglia and thalamus lesions. Recent evidence further points at white matter (WM) damage. This study aims to identify altered WM pathways in dyskinetic CP from a standardized, connectome‐based approach, and to assess structure‐function relationship in WM pathways for clinical outcomes. Individual connectome maps of 25 subjects with dyskinetic CP and 24 healthy controls were obtained combining a structural parcellation scheme with whole‐brain deterministic tractography. Graph theoretical metrics and the network‐based statistic were applied to compare groups and to correlate WM state with motor and cognitive performance. Results showed a widespread reduction of WM volume in CP subjects compared to controls and a more localized decrease in degree (number of links per node) and fractional anisotropy (FA), comprising parieto‐occipital regions and the hippocampus. However, supramarginal gyrus showed a significantly higher degree. At the network level, CP subjects showed a bilateral pathway with reduced FA, comprising sensorimotor, intraparietal and fronto‐parietal connections. Gross and fine motor functions correlated with FA in a pathway comprising the sensorimotor system, but gross motor also correlated with prefrontal, temporal and occipital connections. Intelligence correlated with FA in a network with fronto‐striatal and parieto‐frontal connections, and visuoperception was related to right occipital connections. These findings demonstrate a disruption in structural brain connectivity in dyskinetic CP, revealing general involvement of posterior brain regions with relative preservation of prefrontal areas. We identified pathways in which WM integrity is related to clinical features, including but not limited to the sensorimotor system. Hum Brain Mapp 38:4594–4612, 2017. © 2017 Wiley Periodicals, Inc.     

Resting‐state oscillatory dynamics in sensorimotor cortex in benign epilepsy with centro‐temporal spikes and typical brain development

Benign Epilepsy with Centro‐Temporal Spikes (BECTS) is a common childhood epilepsy associated with deficits in several neurocognitive domains. Neurophysiological studies in BECTS often focus on centro‐temporal spikes, but these correlate poorly with morphology and cognitive impairments. To better understand the neural profile of BECTS, we studied background brain oscillations, thought to be integrally involved in neural network communication, in sensorimotor areas. We used independent component analysis of temporally correlated sources on magnetoencephalography recordings to assess sensorimotor resting‐state network activity in BECTS patients and typically developing controls. We also investigated the variability of oscillatory characteristics within focal primary motor cortex (M1), localized with a separate finger abduction task. We hypothesized that background oscillations would differ between patients and controls in the sensorimotor network but not elsewhere, especially in the beta band (13–30 Hz) because of its role in network communication and motor processing. The results support our hypothesis: in the sensorimotor network, patients had a greater variability in oscillatory amplitude compared to controls, whereas there was no difference in the visual network. Network measures did not correlate with age. The coefficient of variation of resting M1 peak frequency correlated negatively with age in the beta band only, and was greater than average for a number of patients. Our results point toward a “disorganized” functional sensorimotor network in BECTS, supporting a neurodevelopmental delay in sensorimotor cortex. Our findings further suggest that investigating the variability of oscillatory peak frequency may be a useful tool to investigate deficits of disorganization in neurodevelopmental disorders. Hum Brain Mapp 36:3935–3949, 2015. © 2015 Wiley Periodicals, Inc.     

Local and remote effects of transcranial direct current stimulation on the electrical activity of the motor cortical network

We systematically investigated the effects of cathodal and anodal Transcranial Direct Current Stimulation (CtDCS, AtDCS) on the electric activity of primary motor cortex during a motor task. High‐density electroencephalography was used to define the spatial diffusion of tDCS after effects. Ten healthy subjects performed a finger tapping task with the right hand before and after three separate sessions of 20 minutes of Sham, AtDCS or CtDCS over left primary motor cortex (M1). During movement, we found an increment of low alpha band Event‐Related Desynchronization (ERD) in bilateral central, frontal areas and in the left inferior parietal region, as well as an increment of beta ERD in fronto‐central and parieto‐occipital regions, after AtDCs compared to Sham and CtDCS. In the rest pre‐movement period, after Sham as well as AtDCS, we documented an increment of low alpha band power over the course of pre‐ and post‐stimulation recording sessions, localized in the sensorimotor and parieto‐occipital regions. On the contrary, after CtDCS no increment of low alpha power was found. Finally beta band coherence among signals from left sensorimotor cortex and activity of bilateral parietal, occipital and right frontal regions was higher after AtDCS compared with Sham condition. Similarly, theta coherence with parietal and frontal regions was enhanced after AtDCS. We hypothesize that the local modulation of membrane polarization, as well as long‐lasting synaptic modification induced by tDCS over M1, could result in changes of both local band power and functional architecture of the motor network. Hum Brain Mapp 35:2220–2232, 2014. © 2013 Wiley Periodicals, Inc.     

Localizing evoked and induced responses to faces using magnetoencephalography

A rich pattern of responses in frequency, time and space are known to be generated in the visual cortex in response to faces. Recently, a number of studies have used magnetoencephalography (MEG) to try to record these responses non‐invasively – in many cases using source analysis techniques based on the beamforming method. Here we sought both to characterize best practice for measuring face‐specific responses using MEG beamforming, and to determine whether the results produced by the beamformer match evidence from other modalities. We measured activity to visual presentation of face stimuli and phase‐scrambled control stimuli, and performed source analyses of both induced and evoked responses using Synthetic Aperture Magnetometry. We localized the gamma‐band response to bilateral lateral occipital cortex, and both the gamma‐band response and the M170‐evoked response to the right fusiform gyrus. Differences in the gamma‐band response between faces and scrambled stimuli were confined to the frequency range 50–90 Hz; gamma‐band activity at higher frequencies did not differ between the two stimulus categories. We additionally identified a component of the M220‐evoked response – localized to the parieto‐occipital sulcus – which was enhanced for scrambled vs. unscrambled faces. These findings help to establish that MEG beamforming can localize face‐specific responses in time, frequency and space with good accuracy (when validated against established findings from functional magnetic resonance imaging and intracranial recordings), as well as contributing to the establishment of best methodological practice for the use of the beamformer method to measure face‐specific responses.     

Mirror neuron activation as a function of explicit learning: changes in mu‐event‐related power after learning novel responses to ideomotor compatible,partially compatible,and non‐compatible stimuli

Questions regarding the malleability of the mirror neuron system (MNS) continue to be debated. MNS activation has been reported when people observe another person performing biological goal‐directed behaviors, such as grasping a cup. These findings support the importance of mapping goal‐directed biological behavior onto one's motor repertoire as a means of understanding the actions of others. Still, other evidence supports the Associative Sequence Learning (ASL) model which predicts that the MNS responds to a variety of stimuli after sensorimotor learning, not simply biological behavior. MNS activity develops as a consequence of developing stimulus‐response associations between a stimulus and its motor outcome. Findings from the ideomotor literature indicate that stimuli that are more ideomotor compatible with a response are accompanied by an increase in response activation compared to less compatible stimuli; however, non‐compatible stimuli robustly activate a constituent response after sensorimotor learning. Here, we measured changes in the mu‐rhythm, an EEG marker thought to index MNS activity, predicting that stimuli that differ along dimensions of ideomotor compatibility should show changes in mirror neuron activation as participants learn the respective stimulus‐response associations. We observed robust mu‐suppression for ideomotor‐compatible hand actions and partially compatible dot animations prior to learning; however, compatible stimuli showed greater mu‐suppression than partially or non‐compatible stimuli after explicit learning. Additionally, non‐compatible abstract stimuli exceeded baseline only after participants explicitly learned the motor responses associated with the stimuli. We conclude that the empirical differences between the biological and ASL accounts of the MNS can be explained by Ideomotor Theory.     

Memory traces of long‐range coordinated oscillations in the sleeping human brain

Cognition involves coordinated activity across distributed neuronal networks. Neuronal activity during learning triggers cortical plasticity that allows for reorganization of the neuronal network and integration of new information. Animal studies have shown post‐learning reactivation of learning‐elicited neuronal network activity during subsequent sleep, supporting consolidation of the reorganization. However, no previous studies, to our knowledge, have demonstrated reactivation of specific learning‐elicited long‐range functional connectivity during sleep in humans. We here show reactivation of learning‐induced long‐range synchronization of magnetoencephalography power fluctuations in human sleep. Visuomotor learning elicited a specific profile of long‐range cortico‐cortical synchronization of slow (0.1 Hz) fluctuations in beta band (12–30 Hz) power. The parieto‐occipital part of this synchronization profile reappeared in delta band (1–3.5 Hz) power fluctuations during subsequent sleep, but not during the intervening wakefulness period. Individual differences in the reactivated synchronization predicted postsleep performance improvement. The presleep resting‐state synchronization profile was not reactivated during sleep. The findings demonstrate reactivation of long‐range coordination of neuronal activity in humans, more specifically of reactivation of coupling of infra‐slow fluctuations in oscillatory power. The spatiotemporal profile of delta power fluctuations during sleep may subserve memory consolidation by echoing coordinated activation elicited by prior learning. Hum Brain Mapp, 36:67–84, 2015. © 2014 Wiley Periodicals, Inc.     

Hearing and seeing meaning in noise: Alpha,beta, and gamma oscillations predict gestural enhancement of degraded speech comprehension

During face‐to‐face communication, listeners integrate speech with gestures. The semantic information conveyed by iconic gestures (e.g., a drinking gesture) can aid speech comprehension in adverse listening conditions. In this magnetoencephalography (MEG) study, we investigated the spatiotemporal neural oscillatory activity associated with gestural enhancement of degraded speech comprehension. Participants watched videos of an actress uttering clear or degraded speech, accompanied by a gesture or not and completed a cued‐recall task after watching every video. When gestures semantically disambiguated degraded speech comprehension, an alpha and beta power suppression and a gamma power increase revealed engagement and active processing in the hand‐area of the motor cortex, the extended language network (LIFG/pSTS/STG/MTG), medial temporal lobe, and occipital regions. These observed low‐ and high‐frequency oscillatory modulations in these areas support general unification, integration and lexical access processes during online language comprehension, and simulation of and increased visual attention to manual gestures over time. All individual oscillatory power modulations associated with gestural enhancement of degraded speech comprehension predicted a listener's correct disambiguation of the degraded verb after watching the videos. Our results thus go beyond the previously proposed role of oscillatory dynamics in unimodal degraded speech comprehension and provide first evidence for the role of low‐ and high‐frequency oscillations in predicting the integration of auditory and visual information at a semantic level.     

High‐frequency peripheral vibration decreases completion time on a number of motor tasks

A recent theoretical account of motor control proposes that modulation of afferent information plays a role in affecting how readily we can move. Increasing the estimate of uncertainty surrounding the afferent input is a necessary step in being able to move. It has been proposed that an inability to modulate the gain of this sensory information underlies the cardinal symptoms of Parkinson's disease (PD). We aimed to test this theory by modulating the uncertainty of the proprioceptive signal using high‐frequency peripheral vibration, to determine the subsequent effect on motor performance. We investigated if this peripheral stimulus might modulate oscillatory activity over the sensorimotor cortex in order to understand the mechanism by which peripheral vibration can change motor performance. We found that 80 Hz peripheral vibration applied to the right wrist of a total of 54 healthy human participants reproducibly improved performance across four separate randomised experiments on a number of motor control tasks (nine‐hole peg task, box and block test, reaction time task and finger tapping). Improved performance on all motor tasks (except the amplitude of finger tapping) was also seen for a sample of 18PD patients ON medication. EEG data investigating the effect of vibration on oscillatory activity revealed a significant decrease in beta power (15–30 Hz) over the contralateral sensorimotor cortex at the onset and offset of 80 Hz vibration. This finding is consistent with a novel theoretical account of motor initiation, namely that modulating uncertainty of the proprioceptive afferent signal improves motor performance potentially by gating the incoming sensory signal and allowing for top‐down proprioceptive predictions.     

tDCS modulates behavioral performance and the neural oscillatory dynamics serving visual selective attention

Transcranial direct‐current stimulation (tDCS) is a noninvasive method for modulating human brain activity. Although there are several hypotheses about the net effects of tDCS on brain function, the field's understanding remains incomplete and this is especially true for neural oscillatory activity during cognitive task performance. In this study, we examined whether different polarities of occipital tDCS differentially alter flanker task performance and the underlying neural dynamics. To this end, 48 healthy adults underwent 20 min of anodal, cathodal, or sham occipital tDCS, and then completed a visual flanker task during high‐density magnetoencephalography (MEG). The resulting oscillatory responses were imaged in the time‐frequency domain using beamforming, and the effects of tDCS on task‐related oscillations and spontaneous neural activity were assessed. The results indicated that anodal tDCS of the occipital cortices inhibited flanker task performance as measured by reaction time, elevated spontaneous activity in the theta (4–7 Hz) and alpha (9–14 Hz) bands in prefrontal and occipital cortices, respectively, and reduced task‐related theta oscillatory activity in prefrontal cortices during task performance. Cathodal tDCS of the occipital cortices did not significantly affect behavior or any of these neuronal parameters in any brain region. Lastly, the power of theta oscillations in the prefrontal cortices was inversely correlated with reaction time. In conclusion, anodal tDCS modulated task‐related oscillations and spontaneous activity across multiple cortical areas, both near the electrode and in distant sites that were putatively connected to the targeted regions.     

Watching object related movements modulates mirror-like activity in parietal brain regions

ObjectiveWe studied the activation of cortical motor and parietal areas during the observation of object related grasping movements. By manipulating the type of an object (realistic versus abstract) and the type of grasping (correct versus incorrect), we addressed the question how observing such object related movements influences cortical rhythmicity, especially the mu-rhythm, in the context of an “extended” human mirror neuron system (MNS).MethodsMultichannel electroencephalogram (EEG) was recorded during the observation of different object-related grasping actions in twenty healthy subjects. Different movies were presented, showing sequences of correct or incorrect hand grasping actions related to an abstract or realistic (daily life) object.ResultsEvent-related de/synchronization (ERD/ERS) analyses revealed a larger ERD in the upper alpha (10–12 Hz), beta (16–20 Hz) and gamma (36–40 Hz) frequency bands over parietal brain regions depending on the type of grasping. The type of object only influenced ERD patterns in the gamma band range (36–40 Hz) at parietal sites suggesting a strong relation of gamma band activity and cortical object representation. Abstract and realistic objects produced lower beta band synchronization at central sites only, whereas depending on the type of grasping an ERS in the upper alpha band (10–12 Hz) was observed.ConclusionDepending on the type of the grasped object and the type of grasping stronger parietal cortical activation occurred during movement observation.SignificanceDiscussing the results in terms of an “extended” human mirror neuron system (MNS), it could be concluded that beside sensorimotor areas a stronger involvement of parietal brain regions was found depending on the type of object and grasping movement observed.     

Spatiotemporal dynamics of affective picture processing revealed by intracranial high‐gamma modulations

Our comprehension of the neural mechanisms underlying emotional information processing has largely benefited from noninvasive electrophysiological and functional neuroimaging techniques in recent years. However, the spatiotemporal dynamics of the neural events occurring during emotional processing remain imprecise due to the limited combination of spatial and temporal resolution provided by these techniques. This study examines the modulations of high‐frequency activity of intracranial electroencephalography recordings associated with affective picture valence, in epileptic patients awaiting neurosurgery. Recordings were obtained from subdural grids and depth electrodes in eight patients while they viewed a series of unpleasant, pleasant and neutral pictures from the International Affective Picture System. Broadband high‐gamma (70–150 Hz) power was computed for separate 100‐ms time windows and compared according to ratings of emotional valence. Compared to emotionally neutral or pleasant pictures, unpleasant stimuli were associated with an early and long‐lasting (≈200–1,000 ms) bilateral increase in high‐gamma activity in visual areas of the occipital and temporal lobes, together with a late and transient (≈500–800 ms) decrease found bilaterally in the lateral prefrontal cortex (PFC). Pleasant pictures were associated with increased gamma activity in the occipital cortex, compared to the emotionally neutral stimuli. Consistent with previous studies, our results provide direct evidence of emotion‐related modulations in the visual ventral pathway during picture processing. Results in the lateral PFC also shed light on the neural mechanisms underlying its role in negative emotions processing. This study demonstrates the utility of intracranial high‐gamma modulations to study emotional process with a high spatiotemporal precision. Hum Brain Mapp, 36:16–28, 2015.. © 2014 Wiley Periodicals, Inc.     

Nasal respiration entrains neocortical long‐range gamma coherence during wakefulness

Recent studies have shown that slow cortical potentials in archi‐, paleo‐ and neocortex can phase‐lock with nasal respiration. In some of these areas, gamma activity (γ: 30–100 Hz) is also coupled to the animal's respiration. It has been hypothesized that these functional relationships play a role in coordinating distributed neural activity. In a similar way, inter‐cortical interactions at γ frequency have also been associated as a binding mechanism by which the brain generates temporary opportunities necessary for implementing cognitive functions. The aim of the present study is to explore whether nasal respiration entrains inter‐cortical functional interactions at γ frequency during both wakefulness and sleep. Six adult cats chronically prepared for electrographic recordings were employed in this study. Our results show that during wakefulness, slow cortical respiratory potentials are present in the olfactory bulb and several areas of the neocortex. We also found that these areas exhibit cross‐frequency coupling between respiratory phase and γ oscillation amplitude. We demonstrate that respiratory phase modulates the inter‐cortical gamma coherence between neocortical electrode pairs. On the contrary, slow respiratory oscillation and γ cortical oscillatory entrainments disappear during non‐rapid eye movement and rapid eye movement sleep. These results suggest that a single unified phenomenon involves cross‐frequency coupling and long‐range γ coherence across the neocortex. This fact could be related to the temporal binding process necessary for cognitive functions during wakefulness.     

Sensory‐motor brain network connectivity for speech comprehension

The act of listening to speech activates a large network of brain areas. In the present work, a novel data‐driven technique (the combination of independent component analysis and Granger causality) was used to extract brain network dynamics from an fMRI study of passive listening to Words, Pseudo‐Words, and Reverse‐played words. Using this method we show the functional connectivity modulations among classical language regions (Broca's and Wernicke's areas) and inferior parietal, somatosensory, and motor areas and right cerebellum. Word listening elicited a compact pattern of connectivity within a parieto‐somato‐motor network and between the superior temporal and inferior frontal gyri. Pseudo‐Word stimuli induced activities similar to the Word condition, which were characterized by a highly recurrent connectivity pattern, mostly driven by the temporal lobe activity. Also the Reversed‐Word condition revealed an important influence of temporal cortices, but no integrated activity of the parieto‐somato‐motor network. In parallel, the right cerebellum lost its functional connection with motor areas, present in both Word and Pseudo‐Word listening. The inability of the participant to produce the Reversed‐Word stimuli also evidenced two separate networks: the first was driven by frontal areas and the right cerebellum toward somatosensory cortices; the second was triggered by temporal and parietal sites towards motor areas. Summing up, our results suggest that semantic content modulates the general compactness of network dynamics as well as the balance between frontal and temporal language areas in driving those dynamics. The degree of reproducibility of auditory speech material modulates the connectivity pattern within and toward somatosensory and motor areas. Hum Brain Mapp, 2010. © 2009 Wiley‐Liss, Inc.     

Medial prefrontal theta phase coupling during spatial memory retrieval

Memory retrieval is believed to involve a disparate network of areas, including medial prefrontal and medial temporal cortices, but the mechanisms underlying their coordination remain elusive. One suggestion is that oscillatory coherence mediates inter‐regional communication, implicating theta phase and theta‐gamma phase‐amplitude coupling in mnemonic function across species. To examine this hypothesis, we used non‐invasive whole‐head magnetoencephalography (MEG) as participants retrieved the location of objects encountered within a virtual environment. We demonstrate that, when participants are cued with the image of an object whose location they must subsequently navigate to, there is a significant increase in 4–8 Hz theta power in medial prefrontal cortex (mPFC), and the phase of this oscillation is coupled both with ongoing theta phase in the medial temporal lobe (MTL) and perceptually induced 65–85 Hz gamma amplitude in medial parietal cortex. These results suggest that theta phase coupling between mPFC and MTL and theta‐gamma phase‐amplitude coupling between mPFC and neocortical regions may play a role in human spatial memory retrieval. © 2014 The Authors. Hippocampus Published by Wiley Periodicals, Inc.     

Right hemispheric dominance of visual phenomena evoked by intracerebral stimulation of the human visual cortex

Electrical brain stimulation can provide important information about the functional organization of the human visual cortex. Here, we report the visual phenomena evoked by a large number (562) of intracerebral electrical stimulations performed at low‐intensity with depth electrodes implanted in the occipito‐parieto‐temporal cortex of 22 epileptic patients. Focal electrical stimulation evoked primarily visual hallucinations with various complexities: simple (spot or blob), intermediary (geometric forms), or complex meaningful shapes (faces); visual illusions and impairments of visual recognition were more rarely observed. With the exception of the most posterior cortical sites, the probability of evoking a visual phenomenon was significantly higher in the right than the left hemisphere. Intermediary and complex hallucinations, illusions, and visual recognition impairments were almost exclusively evoked by stimulation in the right hemisphere. The probability of evoking a visual phenomenon decreased substantially from the occipital pole to the most anterior sites of the temporal lobe, and this decrease was more pronounced in the left hemisphere. The greater sensitivity of the right occipito‐parieto‐temporal regions to intracerebral electrical stimulation to evoke visual phenomena supports a predominant role of right hemispheric visual areas from perception to recognition of visual forms, regardless of visuospatial and attentional factors. Hum Brain Mapp 35:3360–3371, 2014. © 2013 Wiley Periodicals, Inc .     

Synchronization of gamma oscillations increases functional connectivity of human hippocampus and inferior-middle temporal cortex during repetitive visuomotor events

Do recency processes associated with repetitive sensorimotor events modulate the magnitude and functional coupling of brain rhythmicity in human temporal cortex? Intracranial stereo electroencephalographic activity (SEEG; 256 Hz sampling rate) was recorded from hippocampus, and inferior (BA20) and middle (BA21) temporal cortex in four epilepsy patients. The repetitive events were represented by predicted imperative somatosensory stimuli (CNV paradigm) triggering hand movements (‘repetitive visuomotor’) or counting (‘repetitive counting’). The non‐repetitive events were ‘rare’ (P3 paradigm) somatosensory stimuli triggering hand movements (‘non‐repetitive visuomotor’) or counting (‘non‐repetitive counting’). Brain rhythmicity was indexed by event‐related desynchronization/synchronization (ERD/ERS) of SEEG data, whereas the functional coupling was evaluated by spectral SEEG coherence between pairs of the mentioned areas. The frequency bands of interest were theta (4–8 Hz), alpha (8–12 Hz), beta (14–30 Hz), and gamma (32–46 Hz). Compared to the non‐repetitive events, the ‘repetitive visuomotor’ events showed a significant beta and gamma ERS in the hippocampus and a significant theta ERD in the inferior temporal cortex. Furthermore, the ‘repetitive visuomotor’ events induced a task‐specific significant gamma coherence among the examined areas. These results suggest that recency processes do modulate the magnitude and functional coupling of brain rhythmicity (especially gamma) in the human temporal cortex.     

Movement‐related neuromagnetic fields in preschool age children

We examined sensorimotor brain activity associated with voluntary movements in preschool children using a customized pediatric magnetoencephalographic system. A videogame‐like task was used to generate self‐initiated right or left index finger movements in 17 healthy right‐handed subjects (8 females, ages 3.2–4.8 years). We successfully identified spatiotemporal patterns of movement‐related brain activity in 15/17 children using beamformer source analysis and surrogate MRI spatial normalization. Readiness fields in the contralateral sensorimotor cortex began ～0.5 s prior to movement onset (motor field, MF), followed by transient movement‐evoked fields (MEFs), similar to that observed during self‐paced movements in adults, but slightly delayed and with inverted source polarities. We also observed modulation of mu (8–12 Hz) and beta (15–30 Hz) oscillations in sensorimotor cortex with movement, but with different timing and a stronger frequency band coupling compared to that observed in adults. Adult‐like high‐frequency (70–80 Hz) gamma bursts were detected at movement onset. All children showed activation of the right superior temporal gyrus that was independent of the side of movement, a response that has not been reported in adults. These results provide new insights into the development of movement‐related brain function, for an age group in which no previous data exist. The results show that children under 5 years of age have markedly different patterns of movement‐related brain activity in comparison to older children and adults, and indicate that significant maturational changes occur in the sensorimotor system between the preschool years and later childhood. Hum Brain Mapp 35:4858–4875, 2014. © 2014 Wiley Periodicals, Inc .