Simultaneous recordings of visual evoked potentials and BOLD MRI activations in response to visual motion processing

Patterned edge-illuminated display for clinical examination of visual evoked potentials using simultaneous magnetic resonance imaging

PURPOSE

Commonly used technologies for visual pattern stimulation cannot operate in a magnetic resonance imaging room because they can interfere with the operation of the scanner and are vulnerable to its electromagnetic and magnetic fields. The aim of this single-center prospective observational study was to introduce a novel, structurally uncomplicated, easy-to-maintain, patterned edge-illuminated display (PEID) device for visual pattern-reversal stimulation, compare it with a commonly used cathode ray tube screen, and verify the equivalence of quantitative assays.

MATERIALS AND METHODS

The left and right eyes of 36 healthy participants with undilated pupils were examined on a commercial visual evoked potential (VEP) apparatus and on the PEID device, where pattern-reversal transient VEPs were elicited by checkerboard stimuli with large (0.89°; 0.86°-0.92°) and small (0.21°; 0.20°-0.23°) checks.

RESULTS

The PEID device demonstrated the required reliability and dynamic characteristics, as well as precise time-locking required for a VEP diagnosis. The results of Deming's correlation analysis showed that both the commercial cathode ray tube monitor and the PEID device produced identical VEP results within the context of experimental uncertainty. The standard deviation of Deming's regression may indicate the uncertainty of the VEPs measured in clinical practice. The Bland-Altman analysis of the mean showed no significant difference in the amplitude and peak time of VEPs measured on the PEID device compared to that of the commercial cathode ray tube monitor.

CONCLUSIONS

The presented PEID device meets all the required standards and can be easily installed in various types of commercial magnetic resonance imaging scanners.

Short- and Long-Term Stroboscopic Training Effects on Visuomotor Performance in Elite Youth Sports. Part 2: Brain-Behavior Mechanisms

PURPOSE

Stroboscopic training has repeatedly been shown to improve visuomotor abilities. However, although performance improvements were attributed to visual processes, information on the neurophysiological mechanisms is missing. Part 2 of this study investigated the effects of stroboscopic training on neural visual and motor functions and its contribution to training-induced changes in visuomotor reaction time.

METHODS

Forty-five young elite badminton athletes participated in this study, of which 32 (age, 13.7 yr) were included in the final data analysis. Participants were assigned to an intervention (stroboscopic vision) or control group (normal vision). Before and after a 10-wk training and after a 6-wk retention period, participants performed visual perception and reaction tasks in response to visual motion stimuli. The N2 and N2-r motion onset visual-evoked potentials, its linear combination (Vlc), and the BA6 negativity potential were determined using a 64-channel EEG.

RESULTS

A significant TIME-GROUP effect was observed for the Vlc score (P = 0.019, ηp2 = 0.18), indicating a lower Vlc in the intervention group. However, post hoc tests did not reach significance. Within-subject correlation analyses revealed that changes in reaction speed were related to latency changes in N2 (r = 0.59, P < 0.001), N2-r (r = -0.64, P < 0.001), and the combined Vlc (r = 0.68, P < 0.001). Regression analyses across participants including multiple (N2/N2-r) or single (Vlc) predictors provided an explained variance of >60% (N2/N2-r, r2 = 0.62; Vlc, r2 = 0.64). No training effects or correlations were observed for the BA6 negativity.

CONCLUSIONS

The results indicate that faster visuomotor reactions after stroboscopic training are accompanied by accelerated visual perception and processing, whereas motor processes seemed to be unaffected. Stroboscopic training may be promising to specifically address the visual system in visuomotor-demanding sports.

Visual Perception and Visuomotor Reaction Speed Are Independent of the Individual Alpha Frequency

While the resting-state individual alpha frequency (IAF) is related to the cognitive performance and temporal resolution of visual perception, it remains unclear how it affects the neural correlates of visual perception and reaction processes. This study aimed to unravel the relation between IAF, visual perception, and visuomotor reaction time. One hundred forty-eight (148) participants (28 non-athletes, 39 table tennis players, and 81 badminton players) investigated in three previous studies were considered. During a visuomotor reaction task, the visuomotor reaction time (VMRT) and EMG onset were determined. In addition, a 64-channel EEG system identified the N2, N2-r, and BA6 negativity potentials representing the visual and motor processes related to visuomotor reactions. Resting-state individual alpha frequency (IAF) in visual and motor regions was compared based on sport experience (athletes vs. non-athletes), discipline (badminton vs. table tennis), and reaction performance (fast vs. medium vs. slow reaction time). Further, the differences in the IAF were determined in relation to the speed of neural visual (high vs. medium vs. low N2/N2-r latency) and motor (high vs. medium vs. low BA6 negativity latency). Group comparisons did not reveal any difference in the IAF between athletes and non-athletes (p = 0.352, η _p ² = 0.02) or badminton and table tennis players (p = 0.221, η _p ² = 0.02). Similarly, classification based on the behavioral or neural performance indicators did not reveal any effects on the IAF (p ≥ 0.158, η _p ² ≤ 0.027). IAF was not correlated to any of the behavioral or neural parameters (r ≤ 0.10, p ≥ 0.221). In contrast to behavioral results on cognitive performance and visual temporal resolution, the resting state IAF seemed unrelated to the visual perception and visuomotor reaction speed in simple reaction tasks. Considering the previous results on the correlations between the IAF, cognitive abilities, and temporal sampling of visual information, the results suggest that a higher IAF may facilitate the amount and frequency but not the speed of information transfer.

In vivo functional localization of the temporal monocular crescent representation in human primary visual cortex

The temporal monocular crescent (TMC) is the most peripheral portion of the visual field whose perception relies solely on input from the ipsilateral eye. According to a handful of post-mortem histological studies in humans and non-human primates, the TMC is represented visuotopically within the most anterior portion of the primary visual cortical area (V1). However, functional evidence of the TMC visuotopic representation in human visual cortex is rare, mostly due to the small size of the TMC representation (~6% of V1) and due to the technical challenges of stimulating the most peripheral portion of the visual field inside the MRI scanner. In this study, by taking advantage of custom-built MRI-compatible visual stimulation goggles with curved displays, we successfully stimulated the TMC region of the visual field in eight human subjects, half of them right-eye dominant, inside a 3 ​T MRI scanner. This enabled us to localize the representation of TMC, along with the blind spot representation (another visuotopic landmark in V1), in all volunteers, which match the expected spatial pattern based on prior anatomical studies. In all hemispheres, the TMC visuotopic representation was localized along the peripheral border of V1, within the most anterior portion of the calcarine sulcus, without any apparent extension into the second visual area (V2). We further demonstrate the reliability of this localization within/across experimental sessions, and consistency in the spatial location of TMC across individuals after accounting for inter-subject structural differences.

Electrophysiological evidence of atypical visual change detection in adults with autism

Although atypical change detection processes have been highlighted in the auditory modality in autism spectrum disorder (ASD), little is known about these processes in the visual modality. The aim of the present study was therefore to investigate visual change detection in adults with ASD, taking into account the salience of change, in order to determine whether this ability is affected in this disorder. Thirteen adults with ASD and 13 controls were presented with a passive visual three stimuli oddball paradigm. The findings revealed atypical visual change processing in ASD. Whereas controls displayed a vMMN in response to deviant and a novelty P3 in response to novel stimuli, patients with ASD displayed a novelty P3 in response to both deviant and novel stimuli. These results thus suggested atypical orientation of attention toward unattended minor changes in ASD that might contribute to the intolerance of change.

Electrophysiological correlates of automatic visual change detection in school-age children

Automatic stimulus-change detection is usually investigated in the auditory modality by studying Mismatch Negativity (MMN). Although the change-detection process occurs in all sensory modalities, little is known about visual deviance detection, particularly regarding the development of this brain function throughout childhood. The aim of the present study was to examine the maturation of the electrophysiological response to unattended deviant visual stimuli in 11-year-old children. Twelve children and 12 adults were presented with a passive visual oddball paradigm using dynamic stimuli involving changes in form and motion. Visual Mismatch responses were identified over occipito-parietal sites in both groups but they displayed several differences. In adults the response clearly culminated at around 210 ms whereas in children three successive negative deflections were evidenced between 150 and 330 ms. Moreover, the main mismatch response in children was characterized by a positive component peaking over occipito-parieto-temporal regions around 450 ms after deviant stimulus onset. The findings showed that the organization of the vMMN response is not mature in 11-year-old children and that a longer time is still necessary to process simple visual deviancy at this late stage of child development.

Electrical source dynamics in three functional localizer paradigms

The visual cortex exhibits functional specialization that can be routinely demonstrated using hemodynamic measures like fMRI and PET. To understand the dynamic nature of cortical processes, however, source imaging with a high temporal resolution is necessary. Here, we asked how well distributed EEG source localization (LAURA) identifies functionally specialized visual processes. We tested three stimulus paradigms commonly used in fMRI with the aim to localize striate cortex, motion-sensitive areas, and face-sensitive areas. EEG source localization showed initial activations in striate and extra-striate areas at around 70ms after stimulus onset. These were quickly followed by extensive cortical, as well as subcortical activation. Functional motion and face-selective areas were localized with margins of below 2cm, at around 170 and 150ms, respectively. The results furthermore show for the first time that the C1 component has generators in the insula and frontal eye fields, but also in subcortical areas like the parahippocampus and the thalamus.

Real-time artifact filtering in continuous VEPs/fMRI recording

Continuous recording of Visual Evoked Potentials (VEPs) and functional Magnetic Resonance Imaging (fMRI) exploits the VEPs high temporal resolution and the fMRI high spatial resolution. In this work, we present a new method of continuous VEPs/fMRI recording to study visual function in seven normal subjects. Our real-time artifact filtering is characterized by a procedure based on an analytical study of echo-planar imaging (EPI) sequence parameters related electro-encephalogram (EEG)-artifact shapes. The magnetic field artifacts were minimized by using a dedicated amagnetic device and by a subtraction algorithm that takes into account the EPI sequence parameters. No significant decrease in signal-to-noise ratio was observed in case of EEG recording simultaneously with MR acquisition; similarly, transient and steady-state VEPs parameters were comparable during fMRI acquisition and in the off-phase of fMRI recording. We also applied this method to one patient with optic neuritis, and, compared with controls, found different results. We suggest that our technique can be reliably used to investigate the function of human visual cortex and properly correlate the electrophysiological and functional neuroimaging related changes.

Contact Heat Evoked Potentials Using Simultaneous Eeg And Fmri And Their Correlation With Evoked Pain

BACKGROUND

The Contact Heat Evoked Potential Stimulator (CHEPS) utilises rapidly delivered heat pulses with adjustable peak temperatures to stimulate the differential warm/heat thresholds of receptors expressed by Adelta and C fibres. The resulting evoked potentials can be recorded and measured, providing a useful clinical tool for the study of thermal and nociceptive pathways. Concurrent recording of contact heat evoked potentials using electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) has not previously been reported with CHEPS. Developing simultaneous EEG and fMRI with CHEPS is highly desirable, as it provides an opportunity to exploit the high temporal resolution of EEG and the high spatial resolution of fMRI to study the reaction of the human brain to thermal and nociceptive stimuli.

METHODS

In this study we have recorded evoked potentials stimulated by 51° C contact heat pulses from CHEPS using EEG, under normal conditions (baseline), and during continuous and simultaneous acquisition of fMRI images in ten healthy volunteers, during two sessions. The pain evoked by CHEPS was recorded on a Visual Analogue Scale (VAS).

RESULTS

Analysis of EEG data revealed that the latencies and amplitudes of evoked potentials recorded during continuous fMRI did not differ significantly from baseline recordings. fMRI results were consistent with previous thermal pain studies, and showed Blood Oxygen Level Dependent (BOLD) changes in the insula, post-central gyrus, supplementary motor area (SMA), middle cingulate cortex and pre-central gyrus. There was a significant positive correlation between the evoked potential amplitude (EEG) and the psychophysical perception of pain on the VAS.

CONCLUSION

The results of this study demonstrate the feasibility of recording contact heat evoked potentials with EEG during continuous and simultaneous fMRI. The combined use of the two methods can lead to identification of distinct patterns of brain activity indicative of pain and pro-nociceptive sensitisation in healthy subjects and chronic pain patients. Further studies are required for the technique to progress as a useful tool in clinical trials of novel analgesics.

Cortical Dynamics of Anticipatory Mechanisms in Interception: A Neuromagnetic Study

Humans demonstrate an amazing ability for intercepting and catching moving targets, most noticeably in fast-speed ball games. However, the few studies exploring the neural bases of interception in humans and the classical studies on visual motion processing and visuomotor interactions have reported rather long latencies of cortical activations that cannot explain the performances observed in most natural interceptive actions. The aim of our experiment was twofold: (1) describe the spatio-temporal unfolding of cortical activations involved in catching a moving target and (2) provide evidence that fast cortical responses can be elicited by a visuomotor task with high temporal constraints and decide if these responses are task or stimulus dependent. Neuromagnetic brain activity was recorded with whole-head coverage while subjects were asked to catch a free-falling ball or simply pay attention to the ball trajectory. A fast, likely stimulus-dependent, propagation of neural activity was observed along the dorsal visual pathway in both tasks. Evaluation of latencies of activations in the main cortical regions involved in the tasks revealed that this entire network of regions was activated within 40 msec. Moreover, comparison of experimental conditions revealed similar patterns of activation except in contralateral sensorimotor regions where common and catch-specific activations were differentiated.

Spatiotemporal patterns of oscillatory brain activity during auditory word recognition in children: a synthetic aperture magnetometry study

OBJECTIVE

We studied the task-induced spatiotemporal evolution and characteristics of cortical neural oscillations in children during an auditory word recognition task.

METHODS

We presented abstract nouns binaurally and recorded the MEG response in eight healthy right-handed children (6-12 years). We calculated the event-related changes in cortical oscillations using a beamformer spatial filter analysis technique (SAM), then transformed each subject's statistical maps into standard space and used these to make group statistical inferences.

RESULTS

Across subjects, the cortical response to words could be divided into at least two phases: an initial event-related synchronization in both the right temporal (100-300 ms, 15-25 Hz; 200-400 ms, 5-15 Hz) and left frontal regions (200-400 ms; 15-25 Hz); followed by a strong left-lateralized event-related desynchronization in the left temporal region (500-700 ms; 5-15 Hz).

CONCLUSIONS

We found bilateral event-related synchronization followed by later left lateralized event-related desynchronization in language-related cortical areas. These data demonstrate the spatiotemporal time course of neural activation during an auditory word recognition task in a group of children. As well, this demonstrates the utility of SAM analyses to detect subtle sequential task-related neural activations.

Complex relationship between BOLD signal and synchronization/desynchronization of human brain MEG oscillations

Functional magnetic resonance imaging (fMRI) depends on the coupling of cerebral blood flow, energy demand, and neural activity. The precise nature of this interaction, however, is poorly understood. A positive correlation between BOLD-response and cortically generated local field potentials, which reflect the weighted average of synchronized dentrosomatic components of pyramidal synaptic signals, has been demonstrated. Likewise, positive BOLD-responses have been reported in conjunction with scalp-recorded synchronized electromagnetic activity by a number of groups. However, it is not yet clear how the opposite electromagnetic pattern, i.e. cortical desynchronization, is related to the BOLD signal. To address this question, we conducted a combined event-related fMRI and 275 sensor whole-head MEG study during identical visual two-choice reaction time task conditions in 10 human subjects. We found complex sequences of MEG-synchronization and desynchronization across a wide frequency range in the visual and motor area in close correspondence with "locales" of positive BOLD-responses. These results indicate that a correspondence of positive BOLD-responses is not exclusively found for cortical synchronization but also for desynchronization, suggesting that the relationship between BOLD signals and electromagnetic activity might be more complex than previously thought.

Improved functional mapping of the human amygdala using a standard functional magnetic resonance imaging sequence with simple modifications

As the amygdala is involved in various aspects of emotional processing, its characterization using neuroimaging modalities, such as functional magnetic resonance imaging (fMRI), is of great interest. However, in fMRI, the amygdala region suffers from susceptibility artifacts that are composed of signal dropouts and image distortions. Various technically demanding approaches to reduce these artifacts have been proposed, and most require alterations beyond a mere change of the acquisition parameters and cannot be easily implemented by the user without changing the MR sequence code. In the present study, we therefore evaluated the impact of simple alterations of the acquisition parameters of a standard gradient-echo echo-planar imaging technique at 3 T composed of echo times (TEs) of 27 and 36 ms as well as section thicknesses of 2 and 4 mm while retaining a section orientation parallel to the intercommissural plane and an in-plane resolution of 2x2 mm(2). In contrast to previous studies, we based our evaluation on the resulting activation maps using an emotional stimulation paradigm rather than on MR raw image quality only. Furthermore, we tested the effects of spatial smoothing of the functional raw data in the course of postprocessing using spatial filters of 4 and 8 mm. Regarding MR raw image quality, a TE of 27 ms and 2-mm sections resulted in the least susceptibility artifacts in the anteromedial aspect of the temporal lobe. The emotional stimulation paradigm resulted in robust bilateral amygdala activation for the approaches with 2-mm sections only -- but with larger activation volumes for a TE of 36 ms as compared with that of 27 ms. Moderate smoothing with a 4-mm spatial filter represented a good compromise between increased sensitivity and preserved specificity. In summary, we showed that rather than applying advanced modifications of the MR sequence, a simple increase in spatial resolution (i.e., the reduction of section thickness) is sufficient to improve the detectability of amygdala activation.

A primer on motion visual evoked potentials

Motion visual evoked potentials (motion VEPs) have been used since the late 1960s to investigate the properties of human visual motion processing, and continue to be a popular tool with a possible future in clinical diagnosis. This review first provides a synopsis of the characteristics of motion VEPs and then summarizes important methodological aspects. A subsequent overview illustrates how motion VEPs have been applied to study basic functions of human motion processing and shows perspectives for their use as a diagnostic tool.

Motion-onset VEPs: Characteristics, methods, and diagnostic use

This review article summarises the research on the motion-onset visual evoked potentials (VEPs) and important motion stimulus parameters which have been clarified. For activation of the visual motion processing system and evocation of the motion-onset specific N2 peak (with latency of 160-200ms) from the extra-striate temporo-occipital and/or parietal cortex, the following stimulus parameters can be recently recommended: low luminance (<ca. 20cd/m(2)) and low contrast (<ca. 10%-sinusoidally modulated) of a moving structure with low velocity and temporal frequency (<ca. 6Hz). A short (up to 200ms) duration of motion and a long (at least 1s) inter-stimulus interval reduce adaptation to motion and predominance of a pattern-related P1 peak. Radial motion (with increasing velocity and decreasing spatial frequency towards the periphery) produces larger reactions as compared to a unidirectional translation. In view of the slow maturation (up to the age of 18 years) and early ageing of the visual motion processing system, the use of age-dependent latency norms may be necessary. Since early or selective involvement of the motion processing system is suspected in some CNS disorders, we suggest an evaluation of the utility of motion-onset VEPs as part of the electrophysiological CNS examination since this method may recognise motion processing involvement better than other methods. Motion-onset VEPs might increase the sensitivity of this examination for diagnosing CNS diseases including Multiple Sclerosis, Neuroborreliosis, Glaucoma, Dyslexia and Encephalopathies.