Category-specific occipitotemporal activation during face perception in dyslexic individuals: an MEG study

Reduced categorical learning of faces in dyslexia

The perception of phonological categories in dyslexia is less refined than in typically developing (TD) individuals. Traditionally, this characteristic was considered unique to phonology, yet many studies showed non-phonological perceptual difficulties. Importantly, measuring the dynamics of cortical adaptation, associated with category acquisition, revealed a broadly distributed faster decay of cortical adaptation. Taken together, these observations suggest that the acquisition of perceptual categories in dyslexia may be slower across modalities. To test this, we tested adult individuals with developmental dyslexia (IDDs) and TDs on learning of two unknown faces, yielding face-specific categorization. Initial accuracy was similar in the two groups, yet practice-induced increase in accuracy was significantly larger in TDs. Modeling the learning process (using Drift Diffusion Model) revealed that TDs' steeper learning results from a larger increase in their effective face-specific signal. We propose that IDDs' slower item-specific categorical learning of unknown faces indicates that slower categorical learning in dyslexia is a core, domain-general difficulty.

Let's face it! The role of social anxiety and executive functions in recognizing others' emotions from faces: Evidence from autism and specific learning disorders

Youth with different developmental disorders might experience challenges when dealing with facial emotion recognition (FER). By comparing FER and related emotional and cognitive factors across developmental disorders, researchers can gain a better understanding of challenges and strengths associated with each condition. The aim of the present study was to investigate how social anxiety and executive functioning might underlie FER in youth with and without autism spectrum disorders (ASD) and specific learning disorders (SLD). The study involved 263 children and adolescents between 8 and 16 years old divided into three groups matched for age, sex, and IQ: 60 (52 M) with ASD without intellectual disability, 63 (44 M) with SLD, and 140 (105 M) non-diagnosed. Participants completed an FER test, three executive functions' tasks (inhibition, updating, and set-shifting), and parents filled in a questionnaire reporting their children's social anxiety. Our results suggest that better FER was consistent with higher social anxiety and better updating skills in ASD, while with lower social anxiety in SLD. Clinical practice should focus on coping strategies in autistic youth who could feel anxiety when facing social cues, and on self-efficacy and social worries in SLD. Executive functioning should also be addressed to support social learning in autism.

Atypical reliance on monocular visual pathway for face and word recognition in developmental dyslexia

Studies with individuals with developmental dyslexia (DD) have documented impaired perception of words and faces, both of which are domains of visual expertise for human adults. In this study, we examined a possible mechanism that might be associated with the impaired acquisition of visual expertise for words and faces in DD, namely, the atypical engagement of the monocular visual pathway. Participants with DD and typical readers (TR) judged whether a pair of sequentially presented unfamiliar faces or nonwords were the same or different, and the pair of stimuli were displayed in an eye-specific fashion using a stereoscope. Based on evidence of greater reliance on subcortical structures early in development, we predicted differences between the groups in the engagement of lower (monocular) versus higher (binocular) regions of the visual pathways. Whereas the TR group showed a monocular advantage for both stimulus types, the DD participants evinced a monocular advantage for faces and words that was much greater than that measured in the TRs. These findings indicate that the DD individuals have enhanced subcortical engagement and that this might arise from the failure to fine-tune cortical correlates mediating the discrimination of homogeneous exemplars in domains of expertise.

"Calculating faces": can face perception paradigms enrich dyscalculia research?

Developmental dyscalculia (DD) is a subtype of learning disabilities, which is characterized by lower mathematical skills despite average intelligence and average or satisfactory performance in other academic areas. It is not fully understood how such deficits emerge in the course of brain development. When considering the mechanisms of dyscalculia, two domain-specific systems are distinguished. The Approximate Number System (ANS) is related to the approximate estimation of large sets, and the Object Tracking System (OTS) is responsible for subitizing, that is, the exact quantification of small sets. In recent years, the multiple-deficit framework has become increasingly popular. On the one hand, it explains the impairment of certain general cognitive functions in children with DD, such as executive functions, attention, visual-perceptual discrimination, processing speed, and rapid scanning of visual information. On the other hand, it provides a theoretical basis for explaining the simultaneous occurrence of the different types of other comorbid conditions (such as dyslexia and ADHD) and the relationship between them. We suggest that the face recognition could be considered as another, probably impaired function in dyscalculic individuals. We highlight several brain areas involved both in numerical and facial processing: intraparietal sulcus (IPS), fusiform gyrus (FFG), and hippocampus (HC). We consider the possibility of expanding the scope of dyscalculia research by application of face perception paradigms.

Is It Just Face Blindness? Exploring Developmental Comorbidity in Individuals with Self-Reported Developmental Prosopagnosia

Developmental prosopagnosia (DP)—or ‘face blindness’—refers to life-long problems with facial recognition in the absence of brain injury. We know that neurodevelopmental disorders tend to co-occur, and this study aims to explore if individuals with self-reported DP also report indications of other neurodevelopmental disorders, deficits, or conditions (developmental comorbidity). In total, 115 individuals with self-reported DP participated in this online cross-sectional survey. Face recognition impairment was measured with a validated self-report instrument. Indications of difficulties with navigation, math, reading, or spelling were measured with a tailored questionnaire using items from published sources. Additional diagnoses were measured with direct questions. We also included open-ended questions about cognitive strengths and difficulties. Results: Overall, 57% reported at minimum one developmental comorbidity of interest, with most reflecting specific cognitive impairment (e.g., in memory or object recognition) rather than diagnostic categories (e.g., ADHD, dyslexia). Interestingly, many participants reported cognitive skills or strengths within the same domains that others reported impairment, indicating a diverse pattern of cognitive strengths and difficulties in this sample. The frequency and diversity of self-reported developmental comorbidity suggests that face recognition could be important to consider in future investigations of neurodevelopmental comorbidity patterns.

Faces and words are both associated and dissociated as evidenced by visual problems in dyslexia

Faces and words are traditionally assumed to be independently processed. Dyslexia is also traditionally thought to be a non-visual deficit. Counter to both ideas, face perception deficits in dyslexia have been reported. Others report no such deficits. We sought to resolve this discrepancy. 60 adults participated in the study (24 dyslexic, 36 typical readers). Feature-based processing and configural or global form processing of faces was measured with a face matching task. Opposite laterality effects in these tasks, dependent on left-right orientation of faces, supported that they tapped into separable visual mechanisms. Dyslexic readers tended to be poorer than typical readers at feature-based face matching while no differences were found for global form face matching. We conclude that word and face perception are associated when the latter requires the processing of visual features of a face, while processing the global form of faces apparently shares minimal-if any-resources with visual word processing. The current results indicate that visual word and face processing are both associated and dissociated-but this depends on what visual mechanisms are task-relevant. We suggest that reading deficits could stem from multiple factors, and that one such factor is a problem with feature-based processing of visual objects.

Words as Visual Objects: Neural and Behavioral Evidence for High-Level Visual Impairments in Dyslexia

Developmental dyslexia is defined by reading impairments that are disproportionate to intelligence, motivation, and the educational opportunities considered necessary for reading. Its cause has traditionally been considered to be a phonological deficit, where people have difficulties with differentiating the sounds of spoken language. However, reading is a multidimensional skill and relies on various cognitive abilities. These may include high-level vision—the processes that support visual recognition despite innumerable image variations, such as in viewpoint, position, or size. According to our high-level visual dysfunction hypothesis, reading problems of some people with dyslexia can be a salient manifestation of a more general deficit of high-level vision. This paper provides a perspective on how such non-phonological impairments could, in some cases, cause dyslexia. To argue in favor of this hypothesis, we will discuss work on functional neuroimaging, structural imaging, electrophysiology, and behavior that provides evidence for a link between high-level visual impairment and dyslexia.

Face recognition in developmental dyslexia: evidence for dissociation between faces and words

Developmental dyslexia is primarily a reading disorder, but recent studies have indicated that face processing problems may also be present. Using a case-series approach, we tested face recognition and visual word recognition in 24 high school students diagnosed with developmental dyslexia. Contrary to previous findings, no face recognition problems were found on the group-level. Rather, a significant classical dissociation with impaired word reading and normal face recognition was demonstrated on a group-level and for six individuals with developmental dyslexia. However, four individuals with dyslexia did show face recognition problems. Thus, while problems in face recognition can be present in developmental dyslexia, the dissociation strongly suggests that face recognition can also be preserved. Combined with previously reported dissociations between face and word recognition in developmental prosopagnosia, this constitutes a double dissociation.

Direct behavioral and neural evidence for an offset-triggered conscious perception

Many previous theories of perceptual awareness assume that a conscious representation of a stimulus is created from sensory information carried by an onset (appearance) of the stimulus. In contrast, here we provide behavioral and neural evidence for a new phenomenon in which conscious perception is directly triggered by an offset (disappearance) of a stimulus. When a stimulus made invisible by inter-ocular suppression physically disappeared from a screen, subjects reported an appearance (not disappearance) of that stimulus, correctly reporting a color of the disappeared stimulus. Measurements of brain activity further confirmed that the physical offset of an invisible stimulus evoked neural activity reflecting conscious perception of that stimulus. Those results indicate a new role of a stimulus offset to facilitate (rather than inhibit) an emergence of consciousness.

Structural connectivity patterns associated with the putative visual word form area and children's reading ability

With the advent of neuroimaging techniques, especially functional MRI (fMRI), studies have mapped brain regions that are associated with good and poor reading, most centrally a region within the left occipito-temporal/fusiform region (L-OT/F) often referred to as the visual word form area (VWFA). Despite an abundance of fMRI studies of the putative VWFA, research about its structural connectivity has just started. Provided that the putative VWFA may be connected to distributed regions in the brain, it remains unclear how this network is engaged in constituting a well-tuned reading circuitry in the brain. Here we used diffusion MRI to study the structural connectivity patterns of the putative VWFA and surrounding areas within the L-OT/F in children with typically developing (TD) reading ability and with word recognition deficits (WRD; sometimes referred to as dyslexia). We found that L-OT/F connectivity varied along a posterior-anterior gradient, with specific structural connectivity patterns related to reading ability in the ROIs centered upon the putative VWFA. Findings suggest that the architecture of the putative VWFA connectivity is fundamentally different between TD and WRD, with TD showing greater connectivity to linguistic regions than WRD, and WRD showing greater connectivity to visual and parahippocampal regions than TD. Findings thus reveal clear structural abnormalities underlying the functional abnormalities in the putative VWFA in WRD.

Multiple neural mechanisms for coloring words in synesthesia

Grapheme-color synesthesia is a phenomenon in which achromatic letters/digits automatically induce particular colors. When multiple letters are integrated into a word, some synesthetes perceive that all those letters are changed into the same color, reporting lexical color to that word. Previous psychological studies found several "rules" that determine those lexical colors. The colors to most words are determined by the first letters of the words, while some words in ordinal sequences have their specific colors. Recent studies further reported the third case where lexical colors might be influenced by semantic information of words. Although neural mechanisms determining those lexical colors remained unknown, here we identified three separate neural systems in the synesthete's brain underlying three rules for illusory coloring of words. In addition to the occipito-temporal and parietal regions previously found to be associated with the grapheme-color synesthesia, neural systems for lexical coloring extended to linguistic areas in the left inferior frontal and anterior temporal regions that were engaged in semantic analyses of words. Those results indicate an involvement of wider and higher neural networks than previously assumed in a production of synesthetic colors to visual stimuli and further showed a multiplicity of synesthetic mechanisms represented in the single brain.

Word-specific repetition effects revealed by MEG and the implications for lexical access

This magnetoencephalography (MEG) study investigated the early stages of lexical access in reading, with the goal of establishing when initial contact with lexical information takes place. We identified two candidate evoked responses that could reflect this processing stage: the occipitotemporal N170/M170 and the frontocentral P2. Using a repetition priming paradigm in which long and variable lags were used to reduce the predictability of each repetition, we found that (i) repetition of words, but not pseudowords, evoked a differential bilateral frontal response in the 150-250ms window, (ii) a differential repetition N400m effect was observed between words and pseudowords. We argue that this frontal response, an MEG correlate of the P2 identified in ERP studies, reflects early access to long-term memory representations, which we tentatively characterize as being modality-specific.

Multi-channel atomic magnetometer for magnetoencephalography: a configuration study

Atomic magnetometers are emerging as an alternative to SQUID magnetometers for detection of biological magnetic fields. They have been used to measure both the magnetocardiography (MCG) and magnetoencephalography (MEG) signals. One of the virtues of the atomic magnetometers is their ability to operate as a multi-channel detector while using many common elements. Here we study two configurations of such a multi-channel atomic magnetometer optimized for MEG detection. We describe measurements of auditory evoked fields (AEF) from a human brain as well as localization of dipolar phantoms and auditory evoked fields. A clear N100m peak in AEF was observed with a signal-to-noise ratio of higher than 10 after averaging of 250 stimuli. Currently the intrinsic magnetic noise level is 4fTHz(-1/2) at 10Hz. We compare the performance of the two systems in regards to current source localization and discuss future development of atomic MEG systems.

Cerebral functional asymmetry and phonological performance in dyslexic adults

Developmental dyslexia is a frequent language-based learning disorder characterized by difficulty in reading. The predominant etiologic view postulates that reading impairment is related to phonological and orthographic dysfunction. The aim of this fMRI study was to evaluate the neural bases of phonological processing impairment in remediated dyslexic adults (DD). We used a rhyming words judgment task contrasted with an unreadable fonts font-matching judgment task to compare patterns of activation and functional asymmetry in DD and normal-reading young adults. We found evidence of a link between asymmetry in inferior frontal gyrus and performance during the phonological processing. We also observed that DD recruit a network including regions involved in articulatory control in order to achieve rhyme judgment suggesting that, due to a lack of hemispheric specialization, DD recruit the latter network to achieve rhyme judgment.

Temporal dynamics of neural activity at the moment of emergence of conscious percept

From which regions of the brain do conscious representations of visual stimuli emerge? This is an important but controversial issue in neuroscience because some studies have reported a major role of the higher visual regions of the ventral pathway in conscious perception, whereas others have found neural correlates of consciousness as early as in the primary visual areas and in the thalamus. One reason for this controversy has been the difficulty in focusing on neural activity at the moment when conscious percepts are generated in the brain, excluding any bottom-up responses (not directly related to consciousness) that are induced by stimuli. In this study, we address this issue with a new approach that can induce a rapid change in conscious perception with little influence from bottom-up responses. Our results reveal that the first consciousness-related activity emerges from the higher visual region of the ventral pathway. However, this activity is rapidly diffused to the entire brain, including the early visual cortex. These results thus integrate previous "higher" and "lower" views on the emergence of neural correlates of consciousness, providing a new perspective for the temporal dynamics of consciousness.

Does silent reading speed in normal adult readers depend on early visual processes? evidence from event-related brain potentials

Little is known about the relationship of reading speed and early visual processes in normal readers. Here we examined the association of the early P1, N170 and late N1 component in visual event-related potentials (ERPs) with silent reading speed and a number of additional cognitive skills in a sample of 52 adult German readers utilizing a Lexical Decision Task (LDT) and a Face Decision Task (FDT). Amplitudes of the N170 component in the LDT but, interestingly, also in the FDT correlated with behavioral tests measuring silent reading speed. We suggest that reading speed performance can be at least partially accounted for by the extraction of essential structural information from visual stimuli, consisting of a domain-general and a domain-specific expertise-based portion.

Attentional focus during learning impacts N170 ERP responses to an artificial script

Reading instruction can direct attention to different unit sizes in print-to-speech mapping, ranging from grapheme-phoneme to whole-word relationships. Thus, attentional focus during learning might influence brain mechanisms recruited during reading, as indexed by the N170 response to visual words. To test this, two groups of adults were trained to read an artificial script under instructions directing attention to grapheme-phoneme versus whole-word associations. N170 responses were subsequently contrasted within an active reading task. Grapheme-phoneme focus drove a left-lateralized N170 response relative to the right-lateralized N170 under whole-word focus. These findings suggest a key role for attentional focus in early reading acquisition.

Cortical dynamics of the visual change detection process

In this study, the cortical dynamics of the visual change detection process were investigated using an oddball paradigm similar to that used in auditory mismatch negativity studies. When subjects watched a silent movie, color stimuli were presented using 280 dual color LEDs arranged along the frame of the video screen. Task-irrelevant red and blue color stimuli were presented randomly at a probability of 10% and 90%, respectively, in one session and vice versa for the other one, and we traced brain responses using magnetoencephalography. Results show that activation in the middle occipital gyrus (MOG) was significantly enhanced for the infrequent stimulus, while early activities in Brodmann's area 17/18 were comparable for the frequent and infrequent stimuli. These results suggest that automatic visual change detection is associated with the MOG activity.

Time Course of Activity in Itch-Related Brain Regions: A Combined MEG–fMRI Study

Functional neuroimaging studies have identified itch-related brain regions. However, no study has investigated the temporal aspect of itch-related brain processing. Here this issue was investigated using electrically evoked itch in ten healthy adults. Itch stimuli were applied to the left wrist and brain activity was measured using magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). In the MEG experiment, the magnetic responses evoked by the itch stimuli were observed in the contralateral and ipsilateral frontotemporal regions. The dipoles associated with the magnetic responses were mainly located in the contralateral (nine subjects) and ipsilateral (eight subjects) secondary somatosensory cortex (SII)/insula, which were also activated by the itch stimuli in the fMRI experiment. We also observed an itch-related magnetic response in the posterior part of the centroparietal region in six subjects. MEG and fMRI data showed that the magnetic response in this region was mainly associated with itch-related activation of the precuneus. The latency was significantly longer in the ipsilateral than that in the contralateral SII/insula, suggesting the difference to be associated with transmission in the callosal fibers. The timing of activation of the precuneus was between those of the contralateral and ipsilateral SII/insula. Other sources were located in the premotor, primary motor, and anterior cingulate cortices (one subject each). This study is the first to demonstrate part of the time course of itch-related brain processing. Combining methods with high temporal and spatial resolution (e.g., MEG and fMRI) would be useful to investigate the temporal aspect of the brain mechanism of itch.

The representation and processing of familiar faces in dyslexia: differences in age of acquisition effects

Two under-explored areas of developmental dyslexia research, face naming and age of acquisition (AoA), were investigated. Eighteen dyslexic and 18 non-dyslexic university students named the faces of 50 well-known celebrities, matched for facial distinctiveness and familiarity. Twenty-five of the famous people were learned early in life, while the remaining 25 were first encountered more recently. There was no overall difference between the dyslexics and the non-dyslexics in the speed or the accuracy with which they named faces, suggesting that face naming is unimpaired in dyslexic adults. In keeping with previous findings, the results indicated a speed and accuracy advantage for early-acquired over late-acquired faces. In addition, a significant participant group x AoA interaction demonstrated that the non-dyslexic group was significantly faster to name early- than late-acquired faces, while the dyslexic group showed a much smaller and non-significant effect of AoA. The results suggest that there are differences in representation in dyslexia and that these may be linked to problems with attentional/executive function and automaticity. It is proposed that a more fine-grained approach to investigating dyslexia in adulthood should be adopted, in order to uncover cognitive as well as behavioural differences between dyslexics and non-dyslexics.

Differential orientation effect in the neural response to interacting biological motion of two agents

Background

A recent behavioral study demonstrated that the meaningful interaction of two agents enhances the detection sensitivity of biological motion (BM), however, it remains unclear when and how the 'interaction' information of two agents is represented in our neural system. To clarify this point, we used magnetoencephalography and introduced a novel experimental technique to extract a neuromagnetic response relating to two-agent BM perception. We then investigated how this response was modulated by the interaction of two agents. In the present experiment, we presented two kinds of visual stimuli (interacting and non-interacting BM) with two orientations (upright and inverted).

Results

We found a neuromagnetic response in the bilateral occipitotemporal region, on average 300 – 400 ms after the onset of a two-agent BM stimulus. This result showed that interhemispheric differences were apparent for the peak amplitudes. For the left hemisphere, the orientation effect was manifest when the two agents were made to interact, and the interaction effect was manifest when the stimulus was inverted. In the right hemisphere, the main effects of both orientation and interaction were significant, suggesting that the peak amplitude was attenuated when the visual stimulus was inverted or made to interact.

Conclusion

These results demonstrate that the 'interaction' information of two agents can affect the neural activities in the bilateral occipitotemporal region, on average 300 – 400 ms after the onset of a two-agent BM stimulus, however, the modulation was different between hemispheres: the left hemisphere is more concerned with dynamics, whereas the right hemisphere is more concerned with form information.

Activation of the left inferior frontal gyrus in the first 200 ms of reading: evidence from magnetoencephalography (MEG)

BACKGROUND

It is well established that the left inferior frontal gyrus plays a key role in the cerebral cortical network that supports reading and visual word recognition. Less clear is when in time this contribution begins. We used magnetoencephalography (MEG), which has both good spatial and excellent temporal resolution, to address this question.

METHODOLOGY/PRINCIPAL FINDINGS

MEG data were recorded during a passive viewing paradigm, chosen to emphasize the stimulus-driven component of the cortical response, in which right-handed participants were presented words, consonant strings, and unfamiliar faces to central vision. Time-frequency analyses showed a left-lateralized inferior frontal gyrus (pars opercularis) response to words between 100-250 ms in the beta frequency band that was significantly stronger than the response to consonant strings or faces. The left inferior frontal gyrus response to words peaked at approximately 130 ms. This response was significantly later in time than the left middle occipital gyrus, which peaked at approximately 115 ms, but not significantly different from the peak response in the left mid fusiform gyrus, which peaked at approximately 140 ms, at a location coincident with the fMRI-defined visual word form area (VWFA). Significant responses were also detected to words in other parts of the reading network, including the anterior middle temporal gyrus, the left posterior middle temporal gyrus, the angular and supramarginal gyri, and the left superior temporal gyrus.

CONCLUSIONS/SIGNIFICANCE

These findings suggest very early interactions between the vision and language domains during visual word recognition, with speech motor areas being activated at the same time as the orthographic word-form is being resolved within the fusiform gyrus. This challenges the conventional view of a temporally serial processing sequence for visual word recognition in which letter forms are initially decoded, interact with their phonological and semantic representations, and only then gain access to a speech code.

Discrepancy between reaction time and visual evoked magnetic response latency under priming

We examined effects of the interval between first (S1) and second (S2) visual stimuli, stimulus-onset asynchrony (SOA), on the cortical processing of S2 using magnetoencephalography (MEG). S1 (a circle) and S2 (a cross) were presented at the same location. When the SOA was short (33, 50, and 83 ms), the major deflection of the fields evoked in response to S2 (2M) was difficult to distinguish from that evoked by S1 (1M). However, when the SOA was long (350 and 453 ms), paired stimuli clearly evoked 1M and 2M. At a long SOA, the peak latency of 2M (around 200 ms) was significantly longer than that in the control (S2 alone) condition (around 180 ms). However, in contrast, the reaction time to S2 in all SOA conditions was significantly shortened as compared with that in the control condition, suggesting dissociation between processing in the visual cortex and motor processing.

Temporal Dynamics of Adaptation to Natural Sounds in the Human Auditory Cortex

We aimed at testing the cortical representation of complex natural sounds within auditory cortex by conducting 2 human magnetoencephalography experiments. To this end, we employed an adaptation paradigm and presented subjects with pairs of complex stimuli, namely, animal vocalizations and spectrally matched noise. In Experiment 1, we presented stimulus pairs of same or different animal vocalizations and same or different noise. Our results suggest a 2-step process of adaptation effects: first, we observed a general item-unspecific reduction of the N1m peak amplitude at 100 ms, followed by an item-specific amplitude reduction of the P2m component at 200 ms after stimulus onset for both animal vocalizations and noise. Multiple dipole source modeling revealed the right lateral Heschl's gyrus and the bilateral superior temporal gyrus as sites of adaptation. In Experiment 2, we tested for cross-adaptation between animal vocalizations and spectrally matched noise sounds, by presenting pairs of an animal vocalization and its corresponding or a different noise sound. We observed cross-adaptation effects for the P2m component within bilateral superior temporal gyrus. Thus, our results suggest selectivity of the evoked magnetic field at 200 ms after stimulus onset in nonprimary auditory cortex for the spectral fine structure of complex sounds rather than their temporal dynamics.

The effect of stimulus probability on the somatosensory mismatch field

We investigated the effect of deviant stimulus probability on the somatosensory magnetic mismatch negativity (MMNm) using an electrical two-point stimulation. First, we determined the discrimination threshold (DT) of the two-point distance. We applied standard stimuli at a distance that subjects felt as one point and deviant stimuli at a distance that subjects definitely felt as two points. We used three deviant stimulus probabilities, 10, 30, and 50%. The components peaking around 30-70 ms (first component) and 150-250 ms (fourth component) following deviant stimuli were significantly larger than those following standard stimuli in 10% condition, but not in 30 or 50% condition. The equivalent current dipole (ECD) was located in the contralateral primary somatosensory cortex (cSI) for the first component, and in the cSI and in the contralateral secondary somatosensory cortex (cSII) for the fourth component. The peak amplitude of the MMNm decreased as the probability of the deviant stimulus increased. The Somatosensory MMNm was affected by deviant stimulus probability similar to an auditory mismatch negativity (MMN).

Clinical neurophysiology of language: The MEG approach

Clinical evaluation of language function and basic neuroscience research into the neurophysiology of language are tied together. Whole-head MEG systems readily facilitate detailed spatiotemporal characterization of language processes. A fair amount of information is available about the cortical sequence of word perception and comprehension in the auditory and visual domain, which can be applied for clinical use. Language production remains, at present, somewhat less well charted. In clinical practice, the most obvious needs are noninvasive evaluation of the language-dominant hemisphere and mapping of areas involved in language performance to assist surgery. Multiple experimental designs and analysis approaches have been proposed for estimation of language lateralization. Some of them have been compared with the invasive Wada test and need to be tested further. Development of approaches for more comprehensive pre-surgical characterization of language cortex should build on basic neuroscience research, making use of parametric designs that allow functional mapping. Studies of the neural basis of developmental and acquired language disorders, such as dyslexia, stuttering, and aphasia can currently be regarded more as clinical or basic neuroscience research rather than as clinical routine. Such investigations may eventually provide tools for development of individually targeted training procedures and their objective evaluation.

Objective examination for two-point stimulation using a somatosensory oddball paradigm: An MEG study

OBJECTIVE

To establish an objective two-point discrimination test using magnetoencephalography (MEG).

METHODS

First, we determined the discrimination threshold (DT) of the two-points. In the first experiment, we applied 0.9DT as standard stimuli, and 0.8DT, 1.1DT and 2DT as deviant stimuli in Conditions 1, 2 and 3, respectively. In the second experiment, we used 2DT and 0.9DT as the standard and deviant stimuli, respectively, in Condition 1. We applied two-stimuli that subjects felt as definitely one point or two-points in Condition 2 and 3, respectively.

RESULTS

In the first experiment, the components peaking around 30-70 and 150-250ms following deviant stimuli were significantly larger than those following standard stimuli. Considering the peak latency, these components seem consistent with the magnetic mismatch field (MMF). In the second experiment, the MMF was recorded only in Condition 1. Therefore, it is considered that the MMF was recorded only when subjects automatically discriminate one point from two-points stimuli.

CONCLUSIONS

This novel method can be used in neurophysiological two-point discrimination tests without the need to rely on the examiners' skills and subjects' reactions.

SIGNIFICANCE

We confirmed that our new method could be used for the objective examination of two-point spatial discrimination.

Evidence for a dysfunction of left posterior reading areas in German dyslexic readers

The brain activity during a sentence reading task and a visual control task was examined with fMRI in 13 German dyslexic readers and 15 age-matched fluent readers (age: 14-16 years). These participants came from a longitudinal study and the dyslexic readers exhibited a persistent reading fluency deficit from early on. For the first time with German dyslexic readers, and in correspondence with the majority of functional imaging studies, we found reduced dyslexic activation in the left occipitotemporal cortex and in a small region of the left supramarginal gyrus. Enhanced activation was found in left inferior frontal and subcortical regions.

Backward-masking: The effect of the duration of the second stimulus on recognition of the first stimulus

OBJECTIVE

We recorded event-related magnetic fields following a target stimulus followed by a masking stimulus to investigate the visual backward masking effect using a helmet-type magnetoencephalography system in humans.

METHODS

In the target stimulus with masking stimulus conditions, duration of the target stimulus was constant at 16 ms, and duration of the masking stimulus was altered (16, 48 and 144 ms). The target stimulus was masked by the 144-ms masking stimulus, but not by the 16-ms masking stimulus, and was obscured by the 48-ms masking stimulus. For control conditions (Single-condition), event-related magnetic fields were recorded following the sole presentation of the masking stimulus for 32, 64 or 160 ms.

RESULTS

One major response was obtained at 180 ms after the onset of the stimulation in each condition. The equivalent current dipole of one major response was estimated to lie in the occipital lobe, but there was a relatively large inter-individual difference. There was no significant difference in latency between the target stimulus with masking stimulus conditions and Single-conditions. In the target stimulus with masking stimulus conditions with the 48- and 144-ms masking stimulus, the root mean square value did not differ from that in the respective Single-condition, while the root mean square value for the target stimulus with masking stimulus conditions with the 16-ms masking stimulus was significantly smaller than that in the Single-condition with the 32-ms masking stimulus, but not different from that in the Single-condition with the 16-ms masking stimulus.

CONCLUSIONS

The peak latency of one major response depended on the onset of the first stimulus for both the target stimulus with masking stimulus conditions and Single-condition, but the root mean square value depended on the duration of the masking stimulus. We concluded that the temporal information for the target stimulus was preserved during the masking effect, while the figural information was interrupted by the masking stimulus. Our results suggested that temporal factors for the stimulus were processed differently from those responsible for the object's recognition during backward masking.

Somato-motor inhibitory processing in humans: a study with MEG and ERP

The go/nogo task is a useful paradigm for recording event-related potentials (ERPs) to investigate the neural mechanisms of response inhibition. In nogo trials, a negative deflection at around 140-300 ms (N2), which has been called the 'nogo potential', is elicited at the frontocentral electrodes, compared with ERPs recorded in go trials. In the present study, we investigated the generators of nogo potentials by recording ERPs and by using magnetoencephalography (MEG) simultaneously during somatosensory go/nogo tasks to elucidate the regions involved in generating nogo potentials. ERP data revealed that the amplitude of the nogo-N140 component, which peaked at about 155 ms from frontocentral electrodes, was significantly more negative than that of go-N140. MEG data revealed that a long-latency response peaking at approximately 160 ms, termed nogo-M140 and corresponding to nogo-N140, was recorded in only nogo trials. The equivalent current dipole of nogo-M140 was estimated to lie around the posterior part of the inferior frontal sulci in the prefrontal cortex. These results revealed that both nogo-N140 and nogo-M140 evoked by somatosensory go/nogo tasks were related to the neural activity generated from the prefrontal cortex. Our findings combining MEG and ERPs clarified the spatial and temporal processing related to somato-motor inhibition caused in the posterior part of the inferior frontal sulci in the prefrontal cortex in humans.