Effects of spatially filtered fearful faces and awareness on amygdala activity in adults with autism spectrum disorder: A magnetoencephalography study.

BACKGROUND: The amygdala is pivotal in emotional face processing. Spatial frequencies (SFs) of visual images are divided and processed via two visual pathways: low spatial frequency (LSF) information is conveyed by the magnocellular pathway, while the parvocellular pathway carries high spatial frequency information. We hypothesized that altered amygdala activity might underlie atypical social communication caused by changes in both conscious and non-conscious emotional face processing in the brain in individuals with autism spectrum disorder (ASD). METHOD: Eighteen adults with ASD and 18 typically developing (TD) peers participated in this study. Spatially filtered fearful- and neutral-expression faces and object stimuli were presented under supraliminal or subliminal conditions, and neuromagnetic responses in the amygdala were measured using 306-channel whole-head magnetoencephalography. RESULTS: The latency of the evoked responses at approximately 200 ms to unfiltered neutral face stimuli and object stimuli in the ASD group was shorter than that in the TD group in the unaware condition. Regarding emotional face processing, the evoked responses in the ASD group were larger than those in the TD group under the aware condition. The later positive shift during 200-500 ms (ARV) was larger than that in the TD group, regardless of awareness. Moreover, ARV to HSF face stimuli was larger than that to the other spatial filtered face stimuli in the aware condition. CONCLUSION: Regardless of awareness, ARV might reflect atypical face information processing in the ASD brain.

Asynchronous neural oscillations associated with subliminal affective face priming in autism spectrum disorder.

Autism spectrum disorder (ASD) is characterized by social communicative disturbance. Social communication requires rapid processing and accurate cognition regarding others' emotional expressions. Previous electrophysiological studies have attempted to elucidate the processes underlying atypical face-specific N170 responses to emotional faces in ASD. The present study explored subliminal affective priming effects (SAPEs) on the N170 response and time-frequency analysis of intertrial phase coherence (ITPC) for the N170 in ASD. Fifteen participants [seven participants with ASD and eight typically developing (TD) controls] were recruited for the experiment. Event-related potentials were recorded with a 128-channel electroencephalography device while participants performed an emotional face judgment task. The results revealed enhanced N170 amplitude for supraliminal target-face stimuli when they were preceded by subliminal fearful-face stimuli, in both the ASD and TD groups. Interestingly, TD participants exhibited higher alpha-ITPC in the subliminal fearful-face priming condition in the right face-specific area in the N170 time window. In contrast, there were no significant differences in ITPC in any frequency bands between the subliminal fearful and neutral priming conditions in the ASD group. Asynchronous phase-locking neural activities in the face-specific area may underlie impaired nonconscious face processing in ASD, despite the presence of common features of SAPEs for the N170 component in both the ASD and TD groups.

The effect of interictal epileptic discharges and following spindles on motor sequence learning in epilepsy patients.

Purpose: Interictal epileptic discharges (IEDs) are known to affect cognitive function in patients with epilepsy, but the mechanism has not been elucidated. Sleep spindles appearing in synchronization with IEDs were recently demonstrated to impair memory consolidation in rat, but this has not been investigated in humans. On the other hand, the increase of sleep spindles at night after learning is positively correlated with amplified learning effects during sleep for motor sequence learning. In this study, we examined the effects of IEDs and IED-coupled spindles on motor sequence learning in patients with epilepsy, and clarified their pathological significance. Materials and methods: Patients undergoing long-term video-electroencephalography (LT-VEEG) at our hospital from June 2019 to November 2021 and age-matched healthy subjects were recruited. Motor sequence learning consisting of a finger-tapping task was performed before bedtime and the next morning, and the improvement rate of performance was defined as the sleep-dependent learning effect. We searched for factors associated with the changes in learning effect observed between the periods of when antiseizure medications (ASMs) were withdrawn for LT-VEEG and when they were returned to usual doses after LT-VEEG. Results: Excluding six patients who had epileptic seizures at night after learning, nine patients and 11 healthy subjects were included in the study. In the patient group, there was no significant learning effect when ASMs were withdrawn. The changes in learning effect of the patient group during ASM withdrawal were not correlated with changes in sleep duration or IED density; however, they were significantly negatively correlated with changes in IED-coupled spindle density. Conclusion: We found that the increase of IED-coupled spindles correlated with the decrease of sleep-dependent learning effects of procedural memory. Pathological IED-coupled sleep spindles could hinder memory consolidation, that is dependent on physiological sleep spindles, resulting in cognitive dysfunction in patients with epilepsy.

Unilateral cathodal transcranial direct current stimulation over the parietal area modulates postural control depending with eyes open and closed.

OBJECTIVE: Cathodal transcranial direct current stimulation (C-tDCS) is generally assumed to inhibit cortical excitability. The parietal cortex contributes to multisensory information processing in the postural control system, and this processing is proposed to be different between the right and left hemispheres and sensory modality. However, previous studies did not clarify whether the effects of unilateral C-tDCS of the parietal cortex on the postural control system differ depending on the hemisphere. We investigated the changes in static postural stability after unilateral C-tDCS of the parietal cortex. METHODS: Ten healthy right-handed participants were recruited for right- and left-hemisphere tDCS and sham stimulation, respectively. The cathodal electrode was placed on either the right or left parietal area, whereas the anodal electrode was placed over the contralateral orbit. tDCS was applied at 1.5 mA for 15 min. We evaluated static standing balance by measuring the sway path length (SPL), mediolateral sway path length (ML-SPL), anteroposterior sway path length (AP-SPL), sway area, and the SPL per unit area (L/A) after 15-minute C-tDCS under eyes open (EO) and closed (EC) conditions. To evaluate the effects of C-tDCS on pre- and post-offline trials, each parameter was compared using two-way repeated-measures analysis of variance (ANOVA) with factors of intervention and time. A post-hoc evaluation was performed using a paired t-test. The effect sizes were evaluated according to standardized size-effect indices of partial eta-squared (ηp2) and Cohen's d. The power analysis was calculated (1-ß). RESULTS: A significant interaction was observed between intervention and time for SPL (F (2, 27) = 4.740, p = 0.017, ηp2 = 0.260), ML-SPL (F (2, 27) = 4.926, p = 0.015, ηp2 = 0.267), and sway area (F (2, 27) = 9.624, p = 0.001, ηp2 = 0.416) in the EO condition. C-tDCS over the right hemisphere significantly increased the SPL (p < 0.01, d = 0.51), ML-SPL (p < 0.01, d = 0.52), and sway area (p < 0.05, d = 0.83) in the EO condition. In contrast, C-tDCS over the left hemisphere significantly increased the L/A in both the EC and EO condition (EO; p < 0.05, d = 0.67, EC; p < 0.05, d = 0.57). CONCLUSION: These results suggest that the right parietal region contributes to static standing balance through chiefly visual information processing during the EO condition. On the other hand, L/A increase during EC and EO by tDCS over the left parietal region depends more on somatosensory information to maintain static standing balance during the EC condition.

Large-scale cortico-cerebellar computations for horizontal and vertical vergence in humans.

Horizontal and vertical vergence eye movements play a central role in binocular coordination. Neurophysiological studies suggest that cortical and subcortical regions in animals and humans are involved in horizontal vergence. However, little is known about the extent to which the neural mechanism underlying vertical vergence overlaps with that of horizontal vergence. In this study, to explore neural computation for horizontal and vertical vergence, we simultaneously recorded electrooculography (EOG) and whole-head magnetoencephalography (MEG) while presenting large-field stereograms for 29 healthy human adults. The stereograms were designed to produce vergence responses by manipulating horizontal and vertical binocular disparities. A model-based approach was used to assess neural sensitivity to horizontal and vertical disparities via MEG source estimation and the theta-band (4 Hz) coherence between brain activity and EOG vergence velocity. We found similar time-locked neural responses to horizontal and vertical disparity in cortical and cerebellar areas at around 100-250 ms after stimulus onset. In contrast, the low-frequency oscillatory neural activity associated with the execution of vertical vergence differed from that of horizontal vergence. These findings indicate that horizontal and vertical vergence involve partially shared but distinct computations in large-scale cortico-cerebellar networks.

Phase-dependent modulation of the vestibular-cerebellar network via combined alternating current stimulation influences human locomotion and posture.

Background: Human locomotion induces rhythmic movements of the trunk and head. Vestibular signaling is relayed to multiple regions in the brainstem and cerebellum, and plays an essential role in maintaining head stability. However, how the vestibular-cerebellar network contributes to the rhythmic locomotor pattern in humans is unclear. Transcranial alternating current stimulation (tACS) has been used to investigate the effects of the task-related network between stimulation regions in a phase-dependent manner. Here, we investigated the relationship between the vestibular system and the cerebellum during walking imagery using combined tACS over the left cerebellum and alternating current galvanic vestibular stimulation (AC-GVS). Methods: In Experiment 1, we tested the effects of AC-GVS alone at around individual gait stride frequencies. In Experiment 2, we then determined the phase-specificity of combined stimulation at the gait frequency. Combined stimulation was applied at in-phase (0° phase lag) or anti-phase (180° phase lag) between the left vestibular and left cerebellar stimulation, and the sham stimulation. We evaluated the AC-GVS-induced periodic postural response during walking imagery or no-imagery using the peak oscillatory power on the angular velocity signals of the head in both experiments. In Experiment 2, we also examined the phase-locking value (PLV) between the periodic postural responses and the left AC-GVS signals to estimate entrainment of the postural response by AC-GVS. Results: AC-GVS alone induced the periodic postural response in the yaw and roll axes, but no interactions with imagery walking were observed in Experiment 1 (p > 0.05). By contrast, combined in-phase stimulation increased yaw motion (0.345 ± 0.23) compared with sham (-0.044 ± 0.19) and anti-phase stimulation (-0.066 ± 0.18) during imaginary walking (in-phase vs. other conditions, imagery: p < 0.05; no-imagery: p ≥ 0.125). Furthermore, there was a positive correlation between the yaw peak power of actual locomotion and in-phase stimulation in the imagery session (imagery: p = 0.041; no-imagery: p = 0.177). Meanwhile, we found no imagery-dependent effects in roll peak power or PLV, although in-phase stimulation enhanced roll motion and PLV in Experiment 2. Conclusion: These findings suggest that combined stimulation can influence vestibular-cerebellar network activity, and modulate postural control and locomotion systems in a temporally sensitive manner. This novel combined tACS/AC-GVS stimulation approach may advance development of therapeutic applications.

After-Effects of Intermittent Theta-Burst Stimulation Are Differentially and Phase-Dependently Suppressed by α- and ß-Frequency Transcranial Alternating Current Stimulation.

Intermittent theta-burst stimulation (iTBS) using transcranial magnetic stimulation (TMS) is known to produce excitatory after-effects over the primary motor cortex (M1). Recently, transcranial alternating current stimulation (tACS) at 10 Hz (α) and 20 Hz (ß) have been shown to modulate M1 excitability in a phase-dependent manner. Therefore, we hypothesized that tACS would modulate the after-effects of iTBS depending on the stimulation frequency and phase. To test our hypothesis, we examined the effects of α- and ß-tACS on iTBS using motor evoked potentials (MEPs). Eighteen and thirteen healthy participants were recruited for α and ß tACS conditions, respectively. tACS electrodes were attached over the left M1 and Pz. iTBS over left M1 was performed concurrently with tACS. The first pulse of the triple-pulse burst of iTBS was controlled to match the peak (90°) or trough (270°) phase of the tACS. A sham tACS condition was used as a control in which iTBS was administered without tACS. Thus, each participant was tested in three conditions: the peak and trough of the tACS phases and sham tACS. As a result, MEPs were enhanced after iTBS without tACS (sham condition), as observed in previous studies. α-tACS suppressed iTBS effects at the peak phase but not at the trough phase, while ß-tACS suppressed the effects at both phases. Thus, although both types of tACS inhibited the facilitatory effects of iTBS, only α-tACS did so in a phase-dependent manner. Phase-dependent inhibition by α-tACS is analogous to our previous finding in which α-tACS inhibited MEPs online at the peak condition. Conversely, ß-tACS reduced the effects of iTBS irrespective of its phase. The coupling of brain oscillations and tACS rhythms is considered important in the generation of spike-timing-dependent plasticity. Additionally, the coupling of θ and γ oscillations is assumed to be important for iTBS induction through long-term potentiation (LTP). Therefore, excessive coupling between ß oscillations induced by tACS and γ or θ oscillations induced by iTBS might disturb the coupling of θ and γ oscillations during iTBS. To conclude, the action of iTBS is differentially modulated by neuronal oscillations depending on whether α- or ß-tACS is applied.

Data-point-wise spatiotemporal mapping of human ventral visual areas: Use of spatial frequency/luminance-modulated chromatic faces.

Visual information involving facial identity and expression is crucial for social communication. Although the influence of facial features such as spatial frequency (SF) and luminance on face processing in visual areas has been studied extensively using grayscale stimuli, the combined effects of other features in this process have not been characterized. To determine the combined effects of different SFs and color, we created chromatic stimuli with low, high or no SF components, which bring distinct SF and color information into the ventral stream simultaneously. To obtain neural activity data with high spatiotemporal resolution we recorded face-selective responses (M170) using magnetoencephalography. We used a permutation test procedure with threshold-free cluster enhancement to assess statistical significance while resolving problems related to multiple comparisons and arbitrariness found in traditional statistical methods. We found that time windows with statistically significant threshold levels were distributed differently among the stimulus conditions. Face stimuli containing any SF components evoked M170 in the fusiform gyrus (FG), whereas a significant emotional effect on M170 was only observed with the original images. Low SF faces elicited larger activation of the FG and the inferior occipital gyrus than the original images, suggesting an interaction between low and high SF information processing. Interestingly, chromatic face stimuli without SF first activated color-selective regions and then the FG, indicating that facial color was processed according to a hierarchy in the ventral stream. These findings suggest complex effects of SFs in the presence of color information, reflected in M170, and unveil the detailed spatiotemporal dynamics of face processing in the human brain.

A specific phase of transcranial alternating current stimulation at the ß frequency boosts repetitive paired-pulse TMS-induced plasticity.

Transcranial alternating current stimulation (tACS) at 20 Hz (ß) has been shown to modulate motor evoked potentials (MEPs) when paired with transcranial magnetic stimulation (TMS) in a phase-dependent manner. Repetitive paired-pulse TMS (rPPS) with I-wave periodicity (1.5 ms) induced short-lived facilitation of MEPs. We hypothesized that tACS would modulate the facilitatory effects of rPPS in a frequency- and phase-dependent manner. To test our hypothesis, we investigated the effects of combined tACS and rPPS. We applied rPPS in combination with peak or trough phase tACS at 10 Hz (α) or ß, or sham tACS (rPPS alone). The facilitatory effects of rPPS in the sham condition were temporary and variable among participants. In the ß tACS peak condition, significant increases in single-pulse MEPs persisted for over 30 min after the stimulation, and this effect was stable across participants. In contrast, ß tACS in the trough condition did not modulate MEPs. Further, α tACS parameters did not affect single-pulse MEPs after the intervention. These results suggest that a rPPS-induced increase in trans-synaptic efficacy could be strengthened depending on the ß tACS phase, and that this technique could produce long-lasting plasticity with respect to cortical excitability.

Rapidly spreading seizures arise from large-scale functional brain networks in focal epilepsy.

It remains unclear whether epileptogenic networks in focal epilepsy develop on physiological networks. This work aimed to explore the association between the rapid spread of ictal fast activity (IFA), a proposed biomarker for epileptogenic networks, and the functional connectivity or networks of healthy subjects. We reviewed 45 patients with focal epilepsy who underwent electrocorticographic (ECoG) recordings to identify the patients showing the rapid spread of IFA. IFA power was quantified as normalized beta-gamma band power. Using published resting-state functional magnetic resonance imaging databases, we estimated resting-state functional connectivity of healthy subjects (RSFC-HS) and resting-state networks of healthy subjects (RSNs-HS) at the locations corresponding to the patients' electrodes. We predicted the IFA power of each electrode based on RSFC-HS between electrode locations (RSFC-HS-based prediction) using a recently developed method, termed activity flow mapping. RSNs-HS were identified using seed-based and atlas-based methods. We compared IFA power with RSFC-HS-based prediction or RSNs-HS using non-parametric correlation coefficients. RSFC and seed-based RSNs of each patient (RSFC-PT and seed-based RSNs-PT) were also estimated using interictal ECoG data and compared with IFA power in the same way as RSFC-HS and seed-based RSNs-HS. Spatial autocorrelation-preserving randomization tests were performed for significance testing. Nine patients met the inclusion criteria. None of the patients had reflex seizures. Six patients showed pathological evidence of a structural etiology. In total, we analyzed 49 seizures (2-13 seizures per patient). We observed significant correlations between IFA power and RSFC-HS-based prediction, seed-based RSNs-HS, or atlas-based RSNs-HS in 28 (57.1%), 21 (42.9%), and 28 (57.1%) seizures, respectively. Thirty-two (65.3%) seizures showed a significant correlation with either seed-based or atlas-based RSNs-HS, but this ratio varied across patients: 27 (93.1%) of 29 seizures in six patients correlated with either of them. Among atlas-based RSNs-HS, correlated RSNs-HS with IFA power included the default mode, control, dorsal attention, somatomotor, and temporal-parietal networks. We could not obtain RSFC-PT and RSNs-PT in one patient due to frequent interictal epileptiform discharges. In the remaining eight patients, most of the seizures showed significant correlations between IFA power and RSFC-PT-based prediction or seed-based RSNs-PT. Our study provides evidence that the rapid spread of IFA in focal epilepsy can arise from physiological RSNs. This finding suggests an overlap between epileptogenic and functional networks, which may explain why functional networks in patients with focal epilepsy frequently disrupt.

Gender differences in subliminal affective face priming: A high-density ERP study.

INTRODUCTION: Subliminal affective priming effects (SAPEs) refer to the phenomenon by which the presentation of an affective prime stimulus influences the subsequent affective evaluation of a target stimulus. Previous studies have reported that unconsciously processed stimuli affect behavioral performance more than consciously processed stimuli. However, the impact of SAPEs on the face-specific N170 component is unclear. We studied how SAPEs for fearful faces affected the N170 for subsequent supraliminal target faces using event-related potentials (ERPs). METHODS: Japanese adults (n = 44, 20 females) participated in this study. Subliminal prime faces (neutral or fearful) were presented for 17 ms, followed by a backward mask for 283 ms and 800 ms target faces (neutral, emotionally ambiguous, or fearful). 128-channel ERPs were recorded while participants judged the expression of target faces as neutral or fearful. Response rates and response times were also measured for assessing behavioral alterations. RESULTS: Although the behavioral results revealed no evidence of SAPEs, we found gender-related SAPEs in right N170 amplitude. Specifically, female participants exhibited enhanced right N170 amplitude for emotionally neutral faces primed by fearful faces, while male participants exhibited decreased N170 amplitude in fearful prime trials with fearful target faces. Male participants exhibited significant correlations between N170 amplitude and behavioral response time in the fearful prime-neutral target condition. CONCLUSIONS: Our ERP results suggest the existence of a gender difference in target-face processing preceded by subliminally presented face stimuli in the right occipito-temporal region.

Influence of Static Magnetic Field Stimulation on the Accuracy of Tachystoscopically Presented Line Bisection.

Transcranial static magnetic stimulation (tSMS) has been known to reduce human cortical excitability. Here, we investigated whether tSMS would modulate visuo-spatial cognition in healthy humans. Subjects performed a visuo-spatial task requiring judgements about the symmetry of pre-bisected lines. Visual stimuli consisted of symmetrically or asymmetrically transected lines, tachystoscopically presented for 150 ms on a computer monitor. Task performance was examined before, immediately after, and 10 min after tSMS/sham stimulation of 20 min over the posterior parietal cortex (PPC: P4 from the international 10-20 system) or superior temporal gyrus (STG: C6). Nine out of 16 subjects misjudged pre-bisected lines by consistently underestimating the length of the right-side segment (judging lines to be exactly pre-bisected when the transector was located to the left of the midpoint, or judging the left-side segment to be longer when the transector was located at the midpoint). In these subjects showing a leftward bias, tSMS over the right STG reduced the magnitude of the leftward bias. This did not occur with tSMS over the right PPC or sham stimulation. In the remaining right-biased subjects, no intervention effect was observed with any stimulation. Our findings indicate that application of tSMS over the right STG modulates visuo-spatial cognition in healthy adults.

Secondary somatosensory area is involved in vibrotactile temporal-structure processing: MEG analysis of slow cortical potential shifts in humans.

Purpose: Temporal-structure discrimination is an essential dimension of tactile processing. Exploring object surface by touch generates vibrotactile input with various temporal dynamics, which gives diversity to tactile percepts. Here, we examined whether slow cortical potential shifts (SCPs) (<1 Hz) evoked by long vibrotactile stimuli can reflect active temporal-structure processing.Materials and methods: Vibrotactile-evoked magnetic brain responses were recorded in 10 right-handed healthy volunteers using a piezoelectric-based stimulator and whole-head magnetoencephalography. A series of vibrotactile train stimuli with various temporal structures were delivered to the right index finger. While all trains consisted of identical number (15) of stimuli delivered within a fixed duration (1500 ms), temporal structures were varied by modulating inter-stimulus intervals (ISIs). Participants judged regularity/irregularity of ISI for each train in the active condition, whereas they ignored the stimuli while performing a visual distraction task in the passive condition. We analysed the spatiotemporal features of SCPs and their behaviour using the minimum norm estimates with the dynamic statistical parametric mapping.Results: SCPs were localized to contralateral primary somatosensory area (S1), contralateral superior temporal gyrus, and contralateral as well as ipsilateral secondary somatosensory areas (S2). A significant enhancement of SCPs was observed in the ipsilateral S2 (S2i) in the active condition, whereas such effects were absent in the other regions. We also found a significant larger amplitude difference between the regular- and irregular-stimulus evoked S2i responses during the active condition than during the passive condition.Conclusions: This study suggests that S2 subserves the temporal dimension of vibrotactile processing.

Different hemispheric specialization for face/word recognition: A high-density ERP study with hemifield visual stimulation.

INTRODUCTION: The right fusiform face area (FFA) is important for face recognition, whereas the left visual word fusiform area (VWFA) is critical for word processing. Nevertheless, the early stages of unconscious and conscious face and word processing have not been studied systematically. MATERIALS AND METHODS: To explore hemispheric differences for face and word recognition, we manipulated the visual field (left vs. right) and stimulus duration (subliminal [17 ms] versus supraliminal [300 ms]). We recorded P100 and N170 peaks with high-density ERPs in response to faces/objects or Japanese words/scrambled words in 18 healthy young subjects. RESULTS: Contralateral P100 was larger than ipsilateral P100 for all stimulus types in the supraliminal, but not subliminal condition. The face- and word-N170s were not evoked in the subliminal condition. The N170 amplitude for the supraliminal face stimuli was significantly larger than that for the objects, and right hemispheric specialization was found for face recognition, irrespective of stimulus visual hemifield. Conversely, the supraliminal word-N170 amplitude was not significantly modulated by stimulus type, visual field, or hemisphere. CONCLUSIONS: These results suggest that visual awareness is crucial for face and word recognition. Our study using hemifield stimulus presentation further demonstrates the robust right FFA for face recognition but not the left VWFA for word recognition in the Japanese brain.

Facial identity influences facial expression recognition: A high-density ERP study.

The relationship between facial identity and facial expression processing has long been debated. Although previous facial recognition models indicate that facial identity and facial expression processing are independent, psychological studies using the selective attention task (the Garner paradigm) have revealed an asymmetrical relationship between the perception of identity and emotional expressions in faces: while facial expression does not influence facial identity recognition, facial identity influences facial expression recognition. We used the Garner paradigm and recorded high-density event-related potentials (ERPs) to investigate the influence of facial identity on facial expression recognition. Twenty participants judged the expression of faces, while the irrelevant dimension of identity was either held constant (control condition) or varied (orthogonal condition). We recorded 128-channel EEGs while participants completed the facial expression task. We analyzed the two major components of early visual stages: P1 and N170. ERP results revealed a significant main effect of condition on the N170 latency. These results suggest that facial identity influences facial expression recognition in the N170 that reflects the structural encoding of faces. Thus, information on facial expression might be computed based on the unique structure of individual faces.

SNP Discrimination by Tolane-Modified Peptide Nucleic Acids: Application for the Detection of Drug Resistance in Pathogens.

During the treatment of viral or bacterial infections, it is important to evaluate any resistance to the therapeutic agents used. An amino acid substitution arising from a single base mutation in a particular gene often causes drug resistance in pathogens. Therefore, molecular tools that discriminate a single base mismatch in the target sequence are required for achieving therapeutic success. Here, we synthesized peptide nucleic acids (PNAs) derivatized with tolane via an amide linkage at the N-terminus and succeeded in improving the sequence specificity, even with a mismatched base pair located near the terminal region of the duplex. We assessed the sequence specificities of the tolane-PNAs for single-strand DNA and RNA by UV-melting temperature analysis, thermodynamic analysis, an in silico conformational search, and a gel mobility shift assay. As a result, all of the PNA-tolane derivatives stabilized duplex formation to the matched target sequence without inducing mismatch target binding. Among the different PNA-tolane derivatives, PNA that was modified with a naphthyl-type tolane could efficiently discriminate a mismatched base pair and be utilized for the detection of resistance to neuraminidase inhibitors of the influenza A/H1N1 virus. Therefore, our molecular tool can be used to discriminate single nucleotide polymorphisms that are related to drug resistance in pathogens.

Neuromagnetic correlates of hemispheric specialization for face and word recognition.

The adult human brain appears to have specialized and independent neural systems for the visual processing of faces and words: greater selectivity for faces in the right hemisphere (RH) while greater selectivity for words in the left hemisphere (LH). Nevertheless, the nature of functional differences between the hemispheres is still largely unknown. To elucidate the hemispheric specialization for face and word recognition, event-related magnetic fields (ERFs) were recorded in young adults while they passively viewed faces and words presented either in the right visual field or in the left visual field. If the neural correlates of face recognition and word recognition reflect the same lateralization profile, then the lateralization of the magnetic source of the M170 component should follow a similar profile, with a greater M170 response for faces in the RH and a greater M170 response for words in the LH. We observed the expected finding of a larger M170 in the LH for words. Unexpectedly, a larger M170 response in the RH for faces was not found. Thus, the hemispheric organization of face recognition is different from that of word recognition in terms of specificity.

Transcranial alternating current stimulation of α but not ß frequency sharpens multiple visual functions.

BACKGROUND: Transcranial alternating current stimulation (tACS) can entrain and enhance cortical oscillatory activity in a frequency-dependent manner. In our previous study (Nakazono et al., 2016), 20 Hz (ß) tACS significantly increased excitability of primary motor cortex compared with 10 Hz (α) tACS. α oscillations are a prominent feature of the primary visual cortex (V1) in a resting electroencephalogram. Hence, we investigated whether α and ß tACS can differentially influence multiple visual functions. METHODS: Firstly, we evaluated the after-effects of α and ß tACS on pattern-reversal (PR) and focal-flash (FF) visual evoked potentials (VEPs). Secondly, we determined the relationship between resting α oscillations and PR-VEPs modulated by tACS. Thirdly, the behavioral effects of tACS were assessed by contrast sensitivity. RESULTS: α tACS modulated the amplitudes of PR-VEPs, compared with ß tACS, but did not modulate the FF-VEPs. Time-frequency analysis revealed that α tACS facilitated event-related α phase synchronizations without increasing power, which consequently increased the PR-VEP amplitudes. There was a significant positive correlation between PR-VEP amplitudes and resting α oscillations. These findings suggested that α tACS modulated α oscillations, and affected visual functions of contrast and spatial frequency. Indeed, α tACS also improved subjects' contrast sensitivity at the behavioral level. Conversely, ß tACS increased posterior α activity, but did not change VEP amplitudes. CONCLUSIONS: α tACS can influence different neuronal populations from those influenced by ß tACS. Thus, our results provide evidence that α tACS sharpens multiple visual functions by modulating α oscillations in V1.

Vertical size disparity induces enhanced neural responses in good stereo observers.

Stereoscopic three-dimensional vision requires cortical processing for horizontal binocular disparity between the two eyes' retinal images. Behavioral and theoretical studies suggest that vertical size disparity is used to recover the viewing geometry and to generate the slant of a large surface. However, unlike horizontal disparity, the relation between stereopsis and neural responses to vertical disparity remains controversial. To determine the role of cortical processing for vertical size disparity in stereopsis, we measured neuromagnetic responses to disparities in people with good and poor stereopsis, using magnetoencephalography (MEG). Healthy adult participants viewed stereograms with a horizontal or vertical size disparity, and judged the perceived slant of the pattern. We assessed neural activity in response to disparities in the visual cortex and the phase locking of oscillatory responses including the alpha frequency range using MEG. For participants with good stereopsis, activity in the visual areas was significantly higher in response to vertical size disparity than to horizontal size disparity. The time-frequency analysis revealed that early neural responses to vertical size disparity were more phase-locked in good stereo participants than in poor stereo participants. These results provide neuromagnetic evidence that vertical-size disparity processing plays a role in good stereo vision.