Visuo-motor integration in humans: cortical patterns of response lateralisation and functional connectivity

EEG connectivity in functional brain networks supporting visuomotor integration processes in dominant and non-dominant hand movements

Objective.This study explores the changes in the organization of functional brain networks induced by performing a visuomotor integration task, as revealed by noninvasive spontaneous electroencephalographic traces (EEG).Approach.EEG data were acquired during the execution of the Nine Hole Peg Test (NHPT) with the dominant and non-dominant hands in a group of 44 right-handed volunteers. Both spectral analysis and phase-based connectivity analysis were performed in the theta (ϑ), mu (μ) and beta (ß) bands. Graph Theoretical Analysis (GTA) was also performed to investigate the topological reorganization induced by motor task execution.Main results.Spectral analysis revealed an increase of frontoparietal ϑ power and a spatially diffused reduction ofµand ß contribution, regardless of the hand used. GTA showed a significant increase in network integration induced by movement performed with the dominant limb compared to baseline in the ϑ band. Theµand ß bands were associated with a reduction in network integration during the NHPT. In theµrhythm, this result was more evident for the right-hand movement, while in the ß band, results did not show dependence on the laterality. Finally, correlation analysis highlighted an association between frequency-specific topology measures and task performance for both hands.Significance.Our results show that functional brain networks reorganize during visually guided movements in a frequency-dependent manner, differently depending on the hand used (dominant/non dominant).

Beery VMI performance in autism spectrum disorder

Few studies have examined the visuomotor integration (VMI) abilities of individuals with autism spectrum disorder (ASD). An all-male sample consisting of 56 ASD participants (ages 3-23 years) and 36 typically developing (TD) participants (ages 4-26 years) completed the Beery-Buktenica Developmental Test of Visual-Motor Integration (Beery VMI) as part of a larger neuropsychological battery. Participants were also administered standardized measures of intellectual functioning and the Social Responsiveness Scale (SRS), which assesses autism and autism-like traits. The ASD group performed significantly lower on the Beery VMI and on all IQ measures compared to the TD group. VMI performance was significantly correlated with full scale IQ (FSIQ), performance IQ (PIQ), and verbal IQ (VIQ) in the TD group only. However, when FSIQ was taken into account, no significant Beery VMI differences between groups were observed. Only one TD participant scored 1.5 standard deviations (SDs) below the Beery VMI normative sample mean, in comparison to 21% of the ASD sample. As expected, the ASD group was rated as having significantly higher levels of social impairment on the SRS compared to the TD group across all major domains. However, level of functioning on the SRS was not associated with Berry VMI performance. These findings demonstrate that a substantial number of individuals with ASD experience difficulties compared to TD in performing VMI-related tasks, and that VMI is likely affected by general cognitive ability. The fact that lowered Beery VMI performance occurred only within a subset of individuals with ASD and did not correlate with SRS would indicate that visuomotor deficits are not a core feature of ASD, even though they present at a higher rate of impairment than observed in TD participants.

Cerebral Asymmetry of fMRI-BOLD Responses to Visual Stimulation

Hemispheric asymmetry of a wide range of functions is a hallmark of the human brain. The visual system has traditionally been thought of as symmetrically distributed in the brain, but a growing body of evidence has challenged this view. Some highly specific visual tasks have been shown to depend on hemispheric specialization. However, the possible lateralization of cerebral responses to a simple checkerboard visual stimulation has not been a focus of previous studies. To investigate this, we performed two sessions of blood-oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) in 54 healthy subjects during stimulation with a black and white checkerboard visual stimulus. While carefully excluding possible non-physiological causes of left-to-right bias, we compared the activation of the left and the right cerebral hemispheres and related this to grey matter volume, handedness, age, gender, ocular dominance, interocular difference in visual acuity, as well as line-bisection performance. We found a general lateralization of cerebral activation towards the right hemisphere of early visual cortical areas and areas of higher-level visual processing, involved in visuospatial attention, especially in top-down (i.e., goal-oriented) attentional processing. This right hemisphere lateralization was partly, but not completely, explained by an increased grey matter volume in the right hemisphere of the early visual areas. Difference in activation of the superior parietal lobule was correlated with subject age, suggesting a shift towards the left hemisphere with increasing age. Our findings suggest a right-hemispheric dominance of these areas, which could lend support to the generally observed leftward visual attentional bias and to the left hemifield advantage for some visual perception tasks.

Interhemispheric differences of fMRI responses to visual stimuli in patients with side-fixed migraine aura

Migraine sufferers with aura often report photosensitivity and visual discomfort outside of attacks and many consider bright or flickering light an attack-precipitating factor. The nature of this visual hypersensitivity and its relation to the underlying pathophysiology of the migraine aura is unknown. Using fMRI measurements during visual stimulation we examined the visual cortical responsiveness of patients with migraine with aura. We applied a within-patient design by assessing functional interhemispheric differences in patients consistently experiencing visual aura in the same visual hemifield. We recruited 20 patients with frequent side-fixed visual aura attacks (≥90% of auras occurring in the same visual hemifield) and 20 age and sex matched healthy controls and compared the fMRI blood oxygenation level dependent (BOLD) responses to visual stimulation between symptomatic and asymptomatic hemispheres during the interictal phase and between migraine patients and controls. BOLD responses were selectively increased in the symptomatic hemispheres. This was found in the inferior parietal lobule (P = 0.002), the inferior frontal gyrus (P = 0.003), and the superior parietal lobule (P = 0.017). The affected cortical areas comprise a visually driven functional network involved in oculomotor control, guidance of movement, motion perception, visual attention, and visual spatial memory. The patients also had significantly increased response in the same cortical areas when compared to controls (P < 0.05). We discovered a lateralized alteration of a visually driven functional network in patients with side-fixed aura. These findings suggest a hyperexcitability of the visual system in the interictal phase of migraine with visual aura.

Tracking post-error adaptation in the motor system by transcranial magnetic stimulation

The commission of an error triggers cognitive control processes dedicated to error correction and prevention. Post-error adjustments leading to response slowing following an error ("post-error slowing"; PES) might be driven by changes in excitability of the motor regions and the corticospinal tract (CST). The time-course of such excitability modulations of the CST leading to PES is largely unknown. To track these presumed excitability changes after an error, single pulse transcranial magnetic stimulation (TMS) was applied to the motor cortex ipsilateral to the responding hand, while participants were performing an Eriksen flanker task. A robotic arm with a movement compensation system was used to maintain the TMS coil in the correct position during the experiment. Magnetic pulses were delivered over the primary motor cortex ipsilateral to the active hand at different intervals (150, 300, 450 ms) after correct and erroneous responses, and the motor-evoked potentials (MEP) of the first dorsal interosseous muscle (FDI) contralateral to the stimulated hemisphere were recorded. MEP amplitude was increased 450 ms after the error. Two additional experiments showed that this increase was neither associated to the correction of the erroneous responses nor to the characteristics of the motor command. To the extent to which the excitability of the motor cortex ipsi- and contralateral to the response hand are inversely related, these results suggest a decrease in the excitability of the active motor cortex after an erroneous response. This modulation of the activity of the CST serves to prevent further premature and erroneous responses. At a more general level, the study shows the power of the TMS technique for the exploration of the temporal evolution of post-error adjustments within the motor system.

Modelling neural correlates of working memory: a coordinate-based meta-analysis

Working memory subsumes the capability to memorize, retrieve and utilize information for a limited period of time which is essential to many human behaviours. Moreover, impairments of working memory functions may be found in nearly all neurological and psychiatric diseases. To examine what brain regions are commonly and differently active during various working memory tasks, we performed a coordinate-based meta-analysis over 189 fMRI experiments on healthy subjects. The main effect yielded a widespread bilateral fronto-parietal network. Further meta-analyses revealed that several regions were sensitive to specific task components, e.g. Broca's region was selectively active during verbal tasks or ventral and dorsal premotor cortex were preferentially involved in memory for object identity and location, respectively. Moreover, the lateral prefrontal cortex showed a division in a rostral and a caudal part based on differential involvement in task set and load effects. Nevertheless, a consistent but more restricted "core" network emerged from conjunctions across analyses of specific task designs and contrasts. This "core" network appears to comprise the quintessence of regions, which are necessary during working memory tasks. It may be argued that the core regions form a distributed executive network with potentially generalized functions for focussing on competing representations in the brain. The present study demonstrates that meta-analyses are a powerful tool to integrate the data of functional imaging studies on a (broader) psychological construct, probing the consistency across various paradigms as well as the differential effects of different experimental implementations.

Self-organisation in the human visual system--visuo-motor processing with congenitally abnormal V1 input

Due to an abnormal projection of the temporal retina the albinotic primary visual cortex receives substantial input from the ipsilateral visual field. To test whether representation abnormalities are also evident in higher tier visual, and in motor and somatosensory cortices, brain activity was measured with fMRI in 14 subjects with albinism performing a visuo-motor task. During central fixation, a blue or red target embedded in a distractor array was presented for 250 ms in the left or right visual hemifield. After a delay, the subjects were prompted to indicate with left or right thumb button presses the target presence in the upper or lower hemifield. The fMRI responses were evaluated for different regions of interest concerned with visual, motor and somatosensory processing and compared to previously acquired data from 14 controls. The following results were obtained: (1) in albinism the hit rates in the visuo-motor task were indistinguishable from normal. (2) In area MT and the intraparietal sulcus there was an indication of abnormal lateralisation patterns. (3) Largely normal lateralisation patterns were evident in motor and somatosensory cortices. It is concluded that in human albinism, the abnormal visual field representation is made available for visuo-motor processing with a motor cortex that comprises an essentially normal lateralisation. Consequently, specific adaptations of the mechanisms mediating visuo-motor integration are required in albinism.