The SNARC effect in two dimensions: Evidence for a frontoparallel mental number plane

The existence of an association between numbers and space is known for a long time. The most prominent demonstration of this relationship is the spatial numerical association of response codes (SNARC) effect, describing the fact that participants' reaction times are shorter with the left hand for small numbers and with the right hand for large numbers, when being asked to judge the parity of a number (Dehaene et al., J. Exp. Psychol., 122, 371-396, 1993). The SNARC effect is commonly seen as support for the concept of a mental number line, i.e. a mentally conceived line where small numbers are represented more on the left and large numbers are represented more on the right. The SNARC effect has been demonstrated for all three cardinal axes and recently a transverse SNARC plane has been reported (Chen et al., Exp. Brain Res., 233(5), 1519-1528, 2015). Here, by employing saccadic responses induced by auditory or visual stimuli, we measured the SNARC effect within the same subjects along the horizontal (HM) and vertical meridian (VM) and along the two interspersed diagonals. We found a SNARC effect along HM and VM, which allowed predicting the occurrence of a SNARC effect along the two diagonals by means of linear regression. Importantly, significant differences in SNARC strength were found between modalities. Our results suggest the existence of a frontoparallel mental number plane, where small numbers are represented left and down, while large numbers are represented right and up. Together with the recently described transverse mental number plane our findings provide further evidence for the existence of a three-dimensional mental number space.

The association between alterations of eye movement control and cerebral intrinsic functional connectivity in Parkinson's disease

Patients with Parkinson's disease (PD) present with eye movement disturbances that accompany the cardinal motor symptoms. Previous studies have consistently found evidence that large-scale functional networks are critically involved in eye movement control. We challenged the hypothesis that altered eye movement control in patients with PD is closely related to alterations of whole-brain functional connectivity in association with the neurodegenerative process. Saccadic and pursuit eye movements by video-oculography and 'resting-state' functional MRI (3 Tesla) were recorded from 53 subjects, i.e. 31 patients with PD and 22 matched healthy controls. Video-oculographically, a broad spectrum of eye movement impairments was demonstrated in PD patients vs. controls, including interrupted smooth pursuit, hypometric saccades, and a high distractibility in anti-saccades. Significant correlations between altered oculomotor parameters and functional connectivity measures were observed, i.e. the worse the oculomotor performance was, the more the regional functional connectivity in cortical, limbic, thalamic, cerebellar, and brainstem areas was decreased. Remarkably, decreased connectivity between major nodes of the default mode network was tightly correlated with the prevalence of saccadic intrusions as a measure for distractability. In conclusion, dysfunctional eye movement control in PD seems to be primarily associated with (cortical) executive deficits, rather than being related to the ponto-cerebellar circuits or the oculomotor brainstem nuclei. Worsened eye movement performance together with the potential pathophysiological substrate of decreased intrinsic functional connectivity in predominantly oculomotor-associated cerebral functional networks may constitute a behavioral marker in PD.

The effects of unilateral versus bilateral subthalamic nucleus deep brain stimulation on prosaccades and antisaccades in Parkinson's disease

Unilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) in patients with Parkinson's disease improves skeletomotor function assessed clinically, and bilateral STN DBS improves motor function to a significantly greater extent. It is unknown whether unilateral STN DBS improves oculomotor function and whether bilateral STN DBS improves it to a greater extent. Further, it has also been shown that bilateral, but not unilateral, STN DBS is associated with some impaired cognitive-motor functions. The current study compared the effect of unilateral and bilateral STN DBS on sensorimotor and cognitive aspects of oculomotor control. Patients performed prosaccade and antisaccade tasks during no stimulation, unilateral stimulation, and bilateral stimulation. There were three sets of findings. First, for the prosaccade task, unilateral STN DBS had no effect on prosaccade latency and it reduced prosaccade gain; bilateral STN DBS reduced prosaccade latency and increased prosaccade gain. Second, for the antisaccade task, neither unilateral nor bilateral stimulation had an effect on antisaccade latency, unilateral STN DBS increased antisaccade gain, and bilateral STN DBS increased antisaccade gain to a greater extent. Third, bilateral STN DBS induced an increase in prosaccade errors in the antisaccade task. These findings suggest that while bilateral STN DBS benefits spatiotemporal aspects of oculomotor control, it may not be as beneficial for more complex cognitive aspects of oculomotor control. Our findings are discussed considering the strategic role the STN plays in modulating information in the basal ganglia oculomotor circuit.

Time order reversals and saccades

Ballistic eye movements, or saccades, present a major challenge to the visual system. They generate a rapid blur of movement across the surface of the retinae that is rarely consciously seen, as awareness of input is suppressed around the time of a saccade. Saccades are also associated with a number of perceptual distortions. Here we are primarily interested in a saccade-induced illusory reversal of apparent temporal order. We examine the apparent order of transient targets presented around the time of saccades. In agreement with previous reports, we find evidence for an illusory reversal of apparent temporal order when the second of two targets is presented during a saccade - but this is only apparent for some observers. This contrasts with the apparent salience of targets presented during a saccade, which is suppressed for all observers. Our data suggest that separable processes might underlie saccadic suppressions of salience and saccade-induced reversals of apparent order. We suggest the latter arises when neural transients, normally used for timing judgments, are suppressed due to a saccade - but that this is an insufficient pre-condition. We therefore make the further suggestion, that the loss of a neural transient must be coupled with a specific inferential strategy, whereby some people assume that when they lack a clear impression of event timing, that event must have happened less recently than alternate events for which they have a clear impression of timing.

The temporal dynamics of the distractor in the global effect

In the global effect, saccades are displaced towards a distractor if the latter is near to the target, an effect thought to reflect spatial averaging in neurons of the superior colliculus. The temporal dynamics of the global effect have not been well studied, however. We had twelve subjects perform horizontal saccades to a target in trials in which there were either no distractor or a distractor stimulus located 20° above or below the target. The distractor appeared either simultaneously with the target or preceded it by an interval of between 100 and 800 ms, and was either flashed for only 100 ms or remained visible until the subject responded with a saccade. Both flashed and persistent distractors reduced saccadic latency if they preceded target onset, indicating that subjects could use this cue to prepare saccades in advance. Saccadic endpoint was displaced towards a flashed distractor only if it was simultaneous with the target. However, persistent distractors produced a global effect for both simultaneous presentation and distractor-target intervals of 100 ms, but not for longer intervals. We conclude that the global effect requires of the distractor both a recent onset and persistence of the distractor, and that distractor-related activity decays rapidly within 300 ms.

Opsoclonus in a patient with increased titers of anti-GAD antibody provides proof for the conductance-based model of saccadic oscillations

Paucity in gamma-amino butyric acid (GABA) due to blockage in the action of glutamic acid decarboxylase (GAD), as seen in the syndrome of anti-GAD antibody, causes adult onset cerebellar ataxia, muscle rigidity, and episodic spasms. Downbeat nystagmus, saccadic dysmetria, impaired ocular pursuit, and impaired cancelation of vestibular ocular reflex are typical ocular motor deficits in patients with syndrome of anti-GAD antibody. We describe opsoclonus, in addition to downbeat nystagmus, in a patient with increased titers of anti-GAD antibody. Paucity in GABA leading to disinhibition to Purkinje target neurons at deep cerebellar and vestibular nuclei might have caused downbeat nystagmus in our patient. Anti-GAD antibody can also increase levels of glutamate the precursor of GABA and the substrate for the action of GAD. We propose that opsoclonus might be due to increased levels of glutamate and subsequent hyperexcitability of excitatory and inhibitory burst neurons leading to reverberation in their reciprocally innervating circuit.

Are the visual transients from microsaccades helpful? Measuring the influences of small saccades on contrast sensitivity

Like all saccades, microsaccades cause both spatial and temporal changes in the input to the retina. In space, recent studies have shown that these small shifts precisely relocate a narrow (smaller than the foveola) high-acuity retinal locus on the stimulus. However, it has long been questioned whether the temporal modulations resulting from microsaccades are also beneficial for vision. To address this question, we combined spectral analysis of the visual input to the retina with measurements of contrast sensitivity in humans. Estimation of how different types of eye movements redistribute the power of an otherwise stationary stimulus shows that small saccades contribute more temporal power than ocular drift in the low-frequency range, suggesting a specific role for these movements in the encoding of low spatial frequencies. However, an influence on contrast sensitivity was only found for saccades with amplitudes larger than 30'. Contrast thresholds remained highly similar in the presence and absence of smaller saccades. Furthermore, saccades of all amplitudes, including microsaccades, were strongly suppressed during exposure to the stimulus. These findings do not support an important function of the visual transients caused by microsaccades.

Eye and hand movement strategies in older adults during a complex reaching task

The kinematics of upper limb movements and the coordination of eye and hand movements are affected by ageing. These age differences are exacerbated when task difficulty is increased, but the exact nature of these differences remains to be established. We examined the performance of 12 older adults (mean age = 74) and 11 younger adults (mean age = 20) on a multi-phase prehension task. Participants had to reach for a target ball with their preferred hand, pick it up and place it in a tray, then reach for a second target ball and place that in the same tray. On half the trials (stabilising condition), participants were required to hold the tray just above the surface of the table with their non-preferred hand and keep it as still as possible. Hand and eye movements were recorded. Older adults took longer to complete their movements and reached lower peak velocities than the younger adults. Group differences were most apparent in the stabilising condition, suggesting that the added complexity had a greater effect on the performance of the older adults than the young. During pickup, older adults preferred to make an eye movement to the next target as soon as possible, but spent longer fixating the current target during placement, when accuracy requirements were higher. These latter observations suggest that older adults employed a task-dependent eye movement strategy, looking quickly to the next target to allow more time for planning and execution when possible, but fixating on their hand and successful placement of the ball when necessary.

The diagnostic value of saccades in movement disorder patients: a practical guide and review

Saccades are rapid eye movements designed to shift the fovea to objects of visual interest. Abnormalities of saccades offer important clues in the diagnosis of a number of movement disorders. In this review, we explore the anatomy of horizontal and vertical saccades, discuss practical aspects of their examination, and review how saccadic abnormalities in hyperkinetic and hypokinetic movement disorders aid in diagnosis, with video demonstration of classic examples. Documentation of the ease of saccade initiation, range of motion and conjugacy of saccades, speed and accuracy of saccades, dynamic saccadic trajectory, and the presence or absence of saccadic intrusions and oscillations are important components of this exam. We also provide a practical algorithm to demonstrate the value of saccades in the differential diagnosis of the movement disorders patient.

Saccade abnormalities associated with focal cerebral lesions - How cortical and basal ganglia commands shape saccades in humans

OBJECTIVE

To study saccade abnormalities associated with focal cerebral lesions, including the cerebral cortex and basal ganglia (BG).

METHODS

We studied the latency and amplitude of reflexive and voluntary saccades in 37 patients with focal lesions of the frontal and parietal cortices and BG (caudate and putamen), and 51 age-matched controls, along with the ability to inhibit unwanted reflexive saccades.

RESULTS

Latencies of reflexive saccades were prolonged in patients with parietal lesions involving the parietal eye field (PEF), whereas their amplitude was decreased with parietal or putaminal lesions. In contrast, latency of voluntary saccades was prolonged and their success rate reduced with frontal lesions including the frontal eye field (FEF) or its outflow tract as well as the dorsolateral/medial prefrontal cortex, and caudate lesions, whereas their amplitude was decreased with parietal lesions. Inhibitory control of reflexive saccades was impaired with frontal, caudate and, less prominently, parietal lesions.

CONCLUSIONS

PEF is important in triggering reflexive saccades, also determining their amplitude. Whereas FEF and the caudate emit commands for initiating voluntary saccades, their amplitude is mainly determined by PEF. Commands not only from FEF and dorsolateral/medial prefrontal cortex but also from the caudate and PEF serve to inhibit unnecessary reflexive saccades.

SIGNIFICANCE

The findings suggested how cortical and BG commands shape reflexive and voluntary saccades in humans.

Is multiple system atrophy with cerebellar ataxia (MSA-C) like spinocerebellar ataxia and multiple system atrophy with parkinsonism (MSA-P) like Parkinson's disease? - A saccade study on pathophysiology

OBJECTIVE

Patients with multiple system atrophy (MSA) are classified into those mainly manifesting cerebellar ataxia (MSA-C) and those mainly manifesting parkinsonism (MSA-P). Pathophysiological bases of these subtypes remain unclear. We hypothesized that MSA-C patients would resemble spinocerebellar degeneration patients and MSA-P patients would resemble Parkinson's disease (PD) patients in saccade abnormalities.

METHODS

We recorded visually guided and memory guided saccades (MGS) in 27 MSA-C and 15 MSA-P patients, as well as 50 age-matched normal subjects, 14 spinocerebellar degeneration patients showing pure cerebellar symptoms (SCD) and 61 Parkinson's disease (PD) patients.

RESULTS

Saccade parameters of both tasks showed similar changes with progressing disease in SCD and MSA-C patients, as did those of MSA-C and MSA-P patients, although hypometria was slightly more pronounced in MSA-P. In both subtypes of MSA, latency and success rate of MGS were stable throughout disease stages, whereas they deteriorated progressively with progressing disease in PD.

CONCLUSIONS

Pathophysiology underlying MSA-C and MSA-P is similar as viewed from saccade performance. The MGS performance in MSA was preserved. However, MSA-P patients showed more marked hypometria, suggesting a mixture of basal ganglia pathophysiology.

SIGNIFICANCE

The similarity of saccade performance between MSA-C and MSA-P may reflect common olivopontocerebellar pathology, while the direct pathway of the basal ganglia is relatively spared compared with PD, even in MSA-P.

The art of braking: Post saccadic oscillations in the eye tracker signal decrease with increasing saccade size

Recent research has shown that the pupil signal from video-based eye trackers contains post saccadic oscillations (PSOs). These reflect pupil motion relative to the limbus (Nyström, Hooge, & Holmqvist, 2013). More knowledge about video-based eye tracker signals is essential to allow comparison between the findings obtained from modern systems, and those of older eye tracking technologies (e.g. coils and measurement of the Dual Purkinje Image-DPI). We investigated PSOs in horizontal and vertical saccades of different sizes with two high quality video eye trackers. PSOs were very similar within observers, but not between observers. PSO amplitude decreased with increasing saccade size, and this effect was even stronger in vertical saccades; PSOs were almost absent in large vertical saccades. Based on this observation we conclude that the occurrence of PSOs is related to deceleration at the end of a saccade. That PSOs are saccade size dependent and idiosyncratic is a problem for algorithmic determination of saccade endings. Careful description of the eye tracker, its signal, and the procedure used to extract saccades is required to enable researchers to compare data from different eye trackers.

Why are voluntary head movements in cervical dystonia slow?

INTRODUCTION

Rapid head movements associated with a change in fixation (head saccades) have been reported to be slow in cervical dystonia (CD). Such slowing is typically measured as an increase in time to complete a movement. The mechanisms responsible for this slowing are poorly understood.

METHODS

We measured head saccades in 11 CD patients and 11 healthy subjects using a magnetic search coil technique.

RESULTS

Head saccades in CD took longer to reach a desired target location. This longer duration was due to multiple pauses in the trajectory of the head movement. The head velocity of each segment of the (interrupted) head movement was appropriate for the desired total movement amplitude. The head velocity was, however, higher for the amplitude of the individual interrupted movements. These results suggest that brain programs the proper head movement amplitude, but the movement is interrupted by pathological pauses.

CONCLUSION

Voluntary head saccades have a longer duration in CD due to frequent pauses. The frequent pauses reflect pathological interruptions of normally programmed intended head movement.

Oculomotor performance in children with high-functioning Autism Spectrum Disorders

Sensorimotor issues are of increasing focus in the assessment and treatment of Autism Spectrum Disorders (ASD). The oculomotor system is a sensorimotor network that can provide insights into functional neurobiology and has well-established methodologies for investigation. In this study, we assessed oculomotor performance among children with high functioning ASD and typically developing children, ages 6-12 years. Children with ASD exhibited greater horizontal saccade latency and greater phase lag during vertical smooth pursuit. Saccades and smooth pursuit are mediated by spatially distant brain regions and the long-fiber tracts connecting them, many of which are implicated in ASD. Training paradigms for oculomotor deficits have shown positive outcomes in other clinical populations, and deficits described here may provide useful targets for interventions.

A compact field guide to the study of microsaccades: Challenges and functions

Following a period of quiescence at the end of last century, the study of microsaccades has now regained strong impetus and broad attention within the vision research community. This wave of interest, partly fueled by the advent of user-friendly high-resolution eyetrackers, has attracted researchers and led to novel ideas. Old hypothesis have been revisited and new ones formulated. This article is designed to serve as a practical guide for researchers in the field. Because of the history of the field and the difficulty of measuring very small eye movements, the study of microsaccades presents peculiar challenges. Here, we summarize some of the main challenges and describe methods for assessing and improving the quality of the recordings. Furthermore, we examine how these experimental challenges have influenced analysis of the visual functions of microsaccades and critically review current evidence on three long-debated proposals: the maintenance of fixation, the prevention of visual fading, and the exploration of fine spatial detail.

Scene categorization in Alzheimer's disease: a saccadic choice task

AIMS

We investigated the performance in scene categorization of patients with Alzheimer's disease (AD) using a saccadic choice task.

METHOD

24 patients with mild AD, 28 age-matched controls and 26 young people participated in the study. The participants were presented pairs of coloured photographs and were asked to make a saccadic eye movement to the picture corresponding to the target scene (natural vs. urban, indoor vs. outdoor).

RESULTS

The patients' performance did not differ from chance for natural scenes. Differences between young and older controls and patients with AD were found in accuracy but not saccadic latency.

CONCLUSIONS

The results are interpreted in terms of cerebral reorganization in the prefrontal and temporo-occipital cortex of patients with AD, but also in terms of impaired processing of visual global properties of scenes.

Ipsilesional limb ataxia and truncal ipsipulsion in isolated infarction of the superior cerebellar peduncle

The clinical features of a lesion confined to the superior cerebellar peduncle (SCP) have not been defined well in human. A 92-year-old woman suddenly developed mild dysarthria and severe imbalance from an isolated unilateral SCP infarction, and examination showed ipsiversive ocular torsion, severe ipsilesional limb ataxia, and truncal ipsipulsion. These findings are well consistent with those observed in monkeys when the SCP was severed. In addition to the dentate-rubro-thalamic projections, the SCP appears to contain the fibers involved in the control of eye motion in the roll plane.

Quantitative oculomotor findings in migrainous patients

BACKGROUND

Neurotologic signs and symptoms, especially vestibular symptoms are common in migrainous patients. Involvement of the visual system in migrainures has received a great deal of attention in recent years, but the oculomotor part of the visual system has been largely ignored. The goal of this study was to investigate some parts of the central vestibular system using the oculomotor part of videonystagmographic evaluation, including spontaneous nystagmus, gaze-evoked nystagmus, smooth pursuit, saccade and optokinetic ystagmus interictally in migrainous patients.

METHODS

In this case-control study, 30 patients with migraine and 38 healthy volunteers within the age range of 18-48 years old were included spontaneous nystagmus; gaze-evoked nystagmus in right, left and up sides, smooth pursuit, optokinetic nystagmus using three different velocities and saccade test performed in both groups. The data were analyzed using SPSS for Windows 18.0.

RESULTS

Some parameters of gain and phase and also morphology of the smooth pursuit, velocity of the saccade and slow phase velocity of optokinetic were significantly different in migrainures, although the statistical differences of these parameters were not clinically important as they were in the normal range of a defined device.

CONCLUSION

These results may suggest the presence of subtle otoneurologic abnormalities in migrainous patients that is probably due to the efficiency of oculomotor function with vestibulocerebellar origin.

Saccadic eye movement abnormalities in autism spectrum disorder indicate dysfunctions in cerebellum and brainstem

Background

Individuals with autism spectrum disorder (ASD) show atypical scan paths during social interaction and when viewing faces, and recent evidence suggests that they also show abnormal saccadic eye movement dynamics and accuracy when viewing less complex and non-social stimuli. Eye movements are a uniquely promising target for studies of ASD as their spatial and temporal characteristics can be measured precisely and the brain circuits supporting them are well-defined. Control of saccade metrics is supported by discrete circuits within the cerebellum and brainstem - two brain regions implicated in magnetic resonance (MR) morphometry and histopathological studies of ASD. The functional integrity of these distinct brain systems can be examined by evaluating different parameters of visually-guided saccades.

Methods

A total of 65 participants with ASD and 43 healthy controls, matched on age (between 6 and 44-years-old), gender and nonverbal IQ made saccades to peripheral targets. To examine the influence of attentional processes, blocked gap and overlap trials were presented. We examined saccade latency, accuracy and dynamics, as well as the trial-to-trial variability of participants’ performance.

Results

Saccades of individuals with ASD were characterized by reduced accuracy, elevated variability in accuracy across trials, and reduced peak velocity and prolonged duration. In addition, their saccades took longer to accelerate to peak velocity, with no alteration in the duration of saccade deceleration. Gap/overlap effects on saccade latencies were similar across groups, suggesting that visual orienting and attention systems are relatively spared in ASD. Age-related changes did not differ across groups.

Conclusions

Deficits precisely and consistently directing eye movements suggest impairment in the error-reducing function of the cerebellum in ASD. Atypical increases in the duration of movement acceleration combined with lower peak saccade velocities implicate pontine nuclei, specifically suggesting reduced excitatory activity in burst cells that drive saccades relative to inhibitory activity in omnipause cells that maintain stable fixation. Thus, our findings suggest that both cerebellar and brainstem abnormalities contribute to altered sensorimotor control in ASD.

Electronic supplementary material

The online version of this article (doi:10.1186/2040-2392-5-47) contains supplementary material, which is available to authorized users.

Buildup of spatial information over time and across eye-movements

To interact rapidly and effectively with our environment, our brain needs access to a neural representation of the spatial layout of the external world. However, the construction of such a map poses major challenges, as the images on our retinae depend on where the eyes are looking, and shift each time we move our eyes, head and body to explore the world. Research from many laboratories including our own suggests that the visual system does compute spatial maps that are anchored to real-world coordinates. However, the construction of these maps takes time (up to 500ms) and also attentional resources. We discuss research investigating how retinotopic reference frames are transformed into spatiotopic reference-frames, and how this transformation takes time to complete. These results have implications for theories about visual space coordinates and particularly for the current debate about the existence of spatiotopic representations.

Effects of mild to moderate sedation on saccadic eye movements

Sedatives alter the metrics of saccadic eye movements. If these effects are nonspecific consequences of sedation, like drowsiness and loss of attention to the task, or differ between sedatives is still unresolved. A placebo-controlled multi-step infusion of one of three sedatives, propofol or midazolam, both GABA-A agonists, or dexmedetedomidine, an α2-adrenergic agonist, was adopted to compare the effects of these three drugs in exactly the same experimental conditions. 60 healthy human volunteers, randomly divided in 4 groups, participated in the study. Each infusion step, delivered by a computer-controlled infusion pump, lasted 20min. During the last 10min of each step, the subject executed a saccadic task. Target concentration was doubled at each step. This block was repeated until the subject was too sedated to continue or for a maximum of 6 blocks. Subjects were unaware which infusion they were receiving. A video eye tracker was used to record the movements of the right eye. Saccadic parameters were modeled as a function of block number, estimated sedative plasma concentration, and subjective evaluation of sedation. Propofol and midazolam had strong effects on the dynamics and latency of the saccades. Midazolam, and to a less extent, propofol, caused saccades to become increasingly hypometric. Dexmedetedomidine had less impact on saccadic metrics and presented no changes in saccadic gain. Suppression of the sympathetic system associated with dexmedetomidine has different effects on eye movements from the increased activity of the inhibitory GABA-A receptors by propofol and midazolam even when the subjects reported similar sedation level.

A neuron-based time-optimal controller of horizontal saccadic eye movements

A neural network model of biophysical neurons in the midbrain for controlling oculomotor muscles during horizontal human saccades is presented. Neural circuitry that includes omnipause neuron, premotor excitatory and inhibitory burst neurons, long lead burst neuron, tonic neuron, interneuron, abducens nucleus and oculomotor nucleus is developed to investigate saccade dynamics. The final motoneuronal signals drive a time-optimal controller that stimulates a linear homeomorphic model of the oculomotor plant. To our knowledge, this is the first report on modeling the neural circuits at both premotor and motor stages of neural activity in saccadic systems.

Salient stimulus attracts focus of peri-saccadic mislocalization

Visual localization during saccadic eye movements is prone to error. Flashes shortly before and after the onset of saccades are usually perceived to shift towards the saccade target, creating a "compression" pattern. Typically, the saccade landing point coincides with a salient saccade target. We investigated whether the mislocalization focus follows the actual saccade landing point or a salient stimulus. Subjects made saccades to either a target or a memorized location without target. In some conditions, another salient marker was presented between the initial fixation and the saccade landing point. The experiments were conducted on both black and picture backgrounds. The results show that: (a) when a saccade target or a marker (spatially separated from the saccade landing point) was present, the compression pattern of mislocalization was significantly stronger than in conditions without them, for both black and picture background conditions, and (b) the mislocalization focus tended towards the salient stimulus regardless of whether it was the saccade target or the marker. Our results suggest that a salient stimulus presented in the scene may have an attracting effect and therefore contribute to the non-uniformity of saccadic mislocalization of a probing flash.

Electroencephalographic correlates of working memory deficits in children with Fetal Alcohol Spectrum Disorder using a single-electrode pair recording device

OBJECTIVE

Children with Fetal Alcohol Spectrum Disorder (FASD) exhibit cognitive deficits that can be probed using eye movement tasks. We employed a recently developed, single-sensor electroencephalographic (EEG) recording device in measuring EEG activity during the performance of an eye movement task probing working memory in this population.

METHODS

Children with FASD (n=18) and typically developing children (n=19) performed a memory-guided saccade task requiring the participant to remember the spatial location of one, two or three stimuli. We hypothesized that children with FASD would (i) exhibit performance deficits, particularly at greater mnemonic loads; and (ii) display differences in theta (4-8Hz) and alpha (8-12Hz) frequency band power compared with controls.

RESULTS

Children with FASD failed to perform the task correctly more often than controls when presented with two or three stimuli, and demonstrated related reductions in alpha and theta power.

CONCLUSION

These data suggest that the memory-guided task is sensitive to working memory deficits in children with FASD.

SIGNIFICANCE

Simultaneous recording of EEG activity suggest differing patterns of underlying neural recruitment in the clinical group, consistent with previous literature indicating more cognitive resources are required by children with FASD in order to complete complex tasks correctly.

Developmental improvements in voluntary control of behavior: effect of preparation in the fronto-parietal network?

The ability to prepare for an action improves the speed and accuracy of its performance. While many studies indicate that behavior performance continues to improve throughout childhood and adolescence, it remains unclear whether or how preparatory processes change with development. Here, we used a rapid event-related fMRI design in three age groups (8-12, 13-17, 18-25years) who were instructed to execute either a prosaccade (look toward peripheral target) or an antisaccade (look away from target) task. We compared brain activity within the core fronto-parietal network involved in saccade control at two epochs of saccade generation: saccade preparation related to task instruction versus saccade execution related to target appearance. The inclusion of catch trials containing only task instruction and no target or saccade response allowed us to isolate saccade preparation from saccade execution. Five regions of interest were selected: the frontal, supplementary, parietal eye fields which are consistently recruited during saccade generation, and two regions involved in top down executive control: the dorsolateral prefrontal and anterior cingulate cortices. Our results showed strong evidence that developmental improvements in saccade performance were related to better saccade preparation rather than saccade execution. These developmental differences were mostly attributable to children who showed reduced fronto-parietal activity during prosaccade and antisaccade preparation, along with longer saccade reaction times and more incorrect responses, compared to adolescents and adults. The dorsolateral prefrontal cortex was engaged similarly across age groups, suggesting a general role in maintaining task instructions through the whole experiment. Overall, these findings suggest that developmental improvements in behavioral control are supported by improvements in effectively presetting goal-appropriate brain systems.