Effects of overt and covert attention on the steady-state visual evoked potential

The present study explores whether some single nucleotide polymorphisms (SNPs) within CREB1 (rs2709377 and rs6740584), CREBBP (rs2239317, rs2239316, rs3025702, rs130021, rs130005, rs129974 and rs9392) and CREM (rs1148247, rs4934735, rs12775799, rs6481941 and rs16935888) could be associated with schizophrenia (SKZ) and whether they could predict clinical outcomes in Korean in-patients treated with antipsychotics. Two-hundred twenty one in-patients suffering from SKZ and 170 psychiatrically healthy controls were genotyped for 10 SNPs within CREB1, CREBBP and CREM. All patients were assessed for the severity of illness at baseline and at discharge by means of the Positive and Negative Symptoms Scale (PANSS). Our findings suggest the lack of influence of SNPs under investigation in the present study on the susceptibility to SKZ and on the response to antipsychotics. However, taking into account the several limitations of our study, further research is needed to draw more definitive conclusions.     

Effects of overt and covert attention on the steady-state visual evoked potential

Flickering stimuli evoke an oscillatory brain response with the same frequency as the driving stimulus, the so-called steady-state visual evoked potential (SSVEP). SSVEPs are robust brain signals whose amplitudes are enhanced with attention and thus play a major role in the development and use of non-invasive Brain–Computer Interfaces (BCIs). We compared the modulation of SSVEP amplitudes when subjects directly gazed at a flickering array of static dots (overt attention) to when they covertly shifted attention to the dots keeping their eyes at central fixation. A discrimination task was performed at the attended location to ensure that subjects shifted attention as instructed. Horizontal eye movements (allowed in overt attention but to be avoided in covert attention) were monitored by the horizontal electrooculogram.     

Role of superior colliculus in adaptive eye-head coordination during gaze shifts

The goal of this study was to determine which aspects of adaptive eye-head coordination are implemented upstream or downstream from the motor output layers of the superior colliculus (SC). Two monkeys were trained to perform head-free gaze shifts while looking through a 10 degrees aperture in opaque, head-fixed goggles. This training produced context-dependent alterations in eye-head coordination, including a coordinated pattern of saccade-vestibuloocular reflex (VOR) eye movements that caused eye position to converge toward the aperture, and an increased contribution of head movement to the gaze shift. One would expect the adaptations that were implemented downstream from the SC to be preserved in gaze shifts evoked by SC stimulation. To test this, we analyzed gaze shifts evoked from 19 SC sites in monkey 1 and 38 sites in monkey 2, both with and without goggles. We found no evidence that the goggle paradigm altered the basic gaze position-dependent spatial coding of the evoked movements (i.e., gaze was still coded in an eye-centered frame). However, several aspects of the context-dependent coordination strategy were preserved during stimulation, including the adaptive convergence of final eye position toward the goggles aperture, and the position-dependent patterns of eye and head movement required to achieve this. For example, when initial eye position was offset from the learned aperture location at the time of stimulation, a coordinated saccade-VOR eye movement drove it back to the original aperture, and the head compensated to preserve gaze kinematics. Some adapted amplitude-velocity relationships in eye, gaze, and head movement also may have been preserved. In contrast, context-dependent changes in overall eye and head contribution to gaze amplitude were not preserved during SC stimulation. We conclude that 1) the motor output command from the SC to the brain stem can be adapted to produce different position-dependent coordination strategies for different behavioral contexts, particularly for eye-in-head position, but 2) these brain stem coordination mechanisms implement only the default (normal) level of head amplitude contribution to the gaze shift. We propose that a parallel cortical drive, absent during SC stimulation, is required to adjust the overall head contribution for different behavioral contexts.     

Anterior and superior lateral occipito-temporal cortex responsible for target motion prediction during overt and covert visual pursuit

In smooth-pursuit eye movements (SPEM) with gain close to one, SPEM should be controlled mainly by prediction of target motion because retinal slip is nearly zero. We investigated the neural mechanisms of visual-target prediction by the three fMRI experiments. (1) Overt pursuit task: subjects pursued a sinusoidally moving target which blinked (blink condition) or did not blink (continuous condition). (2) Covert pursuit task: subjects covertly pursued the same target with eyes gazed at fixation point. (3) Attend-to-stationary target task: subjects brought attention on a stationary target with eyes gazed at fixation point. In the overt pursuit task, the SPEM gain and the delay in the blink condition were not very different from the continuous condition, indicating good prediction of the blinking target motion. Activities in the dorsolateral prefrontal, precentral, medial superior frontal, intraparietal, and lateral occipito-temporal cortexes increased in the blink-continuous subtraction. The V1 activity decreased for this contrast. In the covert pursuit task, only the anterior/superior LOTC activity remained in the blink-continuous subtraction. In the attend-to-stationary target task, the blink-continuous subtraction elicited no activation. Consequently, the a/sLOTC activity is responsible for target prediction rather than motor commands for eye movements or just target blinking such as visual saliency.     

The instructed context of a motor task modulates covert response preparation and shifts of spatial attention

We investigated how covert response preparation is modulated by the instructed cognitive context of a motor task. Participants prepared left-hand or right-hand movements toward or away from the body midline, as indicated by a response cue (S1) presented prior to a go/no-go stimulus (S2). Different participants were instructed that response cues specified the response hand or movement direction, respectively. This emphasis on effector versus movement direction selection modulated lateralized ERP components triggered during the S1–S2 interval. Attention shifts during movement preparation were assessed by measuring ERPs to irrelevant visual probes. Enhanced N1 components were found for probes near the effector when effector selection was emphasized, but for probes near the movement target location when movement direction selection was emphasized. Results demonstrate strong top-down contextual biases on motor control and on the locus of spatial attention during response preparation.     

The development of grasping comprehension in infancy: covert shifts of attention caused by referential actions

An eye tracking paradigm was used to investigate how infants’ attention is modulated by observed goal-directed manual grasping actions. In Experiment 1, we presented 3-, 5-, and 7-month-old infants with a static picture of a grasping hand, followed by a target appearing at a location either congruent or incongruent with the grasping direction of the hand. The latency of infants gaze shift from the hand to the target was recorded and compared between congruent and incongruent trials. Results demonstrate a congruency effect from 5 months of age. A second experiment illustrated that the congruency effect of Experiment 1 does not extend to a visually similar mechanical claw (instead of the grasping hand). Together these two experiments describe the onset of covert attention shifts in response to manual actions and relate these findings to the onset of manual grasping.     

On-line compensation of gaze shifts perturbed by micro-stimulation of the superior colliculus in the cat with unrestrained head

Prior studies have led to the gaze feedback hypothesis, which states that quick orienting movements of the visual axis (gaze shifts) are controlled by a feedback system. We have previously provided evidence for this hypothesis by extending the original study of Mays and Sparks (1980) to the cat with unrestrained head (Pélisson et al. 1989). We showed that cats compensated for a stimulation-induced perturbation of initial gaze position by generating, in the dark, an accurate gaze shift towards the remembered location of a flashed target. In the present study, we investigate goal-directed gaze shifts perturbed in flight by a brief stimulation of the superior colliculus. The microstimulation parameters were tuned such that significant perturbations were induced without halting the movement. The ambient light was turned off at the onset of the gaze shift, suppressing any visual feedback. We observed that, following stimulation offset, the gaze shift showed temporal and spatial changes in its trajectory to compensate for the transient perturbation. Such compensations, which occurred on-line before gaze shift termination, involved both eye and head movements and had dynamic characteristics resembling those of unperturbed saccadic gaze shifts. These on-line compensations maintained gaze accuracy when the stimulation was applied during the early phase of large and medium (about 60 and 40°) movements. These results are compatible with the notion of a gaze feedback loop providing a dynamic gaze error signal.     

Location and features of instructive spatial cues do not influence the time course of covert shifts of visual spatial attention

The time course of shifting visual spatial attention to flickering stimuli in the left and right visual hemifield was investigated. The goal was to test whether an instructive peripheral salient cue located close to the newly to-be-attended location triggers faster shifts per se compared to a central cue. Besides behavioural data an objective electrophysiological measure, the steady-state visual evoked potential (SSVEP) was used to measure the time course of visual pathway facilitation in the human brain for centrally and peripherally cued shifts of spatial attention. Results revealed that both spatial cues resulted in identical time courses of shifts of covert spatial attention. This was true with respect to behavioural data and SSVEP amplitude. Results support the notion that a salient peripheral spatial cue does not automatically produce faster shifts of spatial attention to the to-be-attended location when this cue is informative and embedded in an ongoing stimulation.     

A survey of paramenstrual complaints by covert and by overt methods

A covert method of assessing perception of health in relation to menstruation was applied prospectively to a group of women aged 20 to 40 years. Of the 1386 randomly selected women contacted, 838 (60%) provided information for the full study period of six weeks and 608 of these respondents menstruated during that time. A clear excess of women demonstrated premenstrual deterioration in perceived health. This rose to a peak at the onset of menstruation and subsided rapidly during menstruation, thus reflecting the conventionally defined pattern of the premenstrual syndrome.

When, on completion of prospective recording, the same women were asked to return an overt and retrospective assessment of paramenstrual symptoms, the overall pattern of results was similar but, for individual women, there was little correspondence between similar data obtained by the two different methods.

     

Kinematics and eye–head coordination of gaze shifts evoked from different sites in the superior colliculus of the cat

Shifting gaze requires precise coordination of eye and head movements. It is clear that the superior colliculus (SC) is involved with saccadic gaze shifts. Here we investigate its role in controlling both eye and head movements during gaze shifts. Gaze shifts of the same amplitude can be evoked from different SC sites by controlled electrical microstimulation. To describe how the SC coordinates the eye and the head, we compare the characteristics of these amplitude-matched gaze shifts evoked from different SC sites. We show that matched amplitude gaze shifts elicited from progressively more caudal sites are progressively slower and associated with a greater head contribution. Stimulation at more caudal SC sites decreased the peak velocity of the eye but not of the head, suggesting that the lower peak gaze velocity for the caudal sites is due to the increased contribution of the slower-moving head. Eye–head coordination across the SC motor map is also indicated by the relative latencies of the eye and head movements. For some amplitudes of gaze shift, rostral stimulation evoked eye movement before head movement, whereas this reversed with caudal stimulation, which caused the head to move before the eyes. These results show that gaze shifts of similar amplitude evoked from different SC sites are produced with different kinematics and coordination of eye and head movements. In other words, gaze shifts evoked from different SC sites follow different amplitude–velocity curves, with different eye–head contributions. These findings shed light on mechanisms used by the central nervous system to translate a high-level motor representation (a desired gaze displacement on the SC map) into motor commands appropriate for the involved body segments (the eye and the head).     

Nystagmus after unilateral injury to the superior colliculus in rabbits

The frequency of optokinetic (OKN) and reversive postoptokinetic (RPN) nystagmus was studied in rabbits before and 7 days after coagulation of the left superior colliculus. After coagulation the frequency of OKN was reduced by 2.7 times and its amplitude by 1.3 times in response to optokinetic stimulation of the right eye after coagulation. During stimulation of the left eye (the retino-collicular tract to this eye was intact) OKN was unchanged or its frequency was increased. The frequency and amplitude of RPN also were reduced after the operation, but by a lesser degree than OKN. The retino-collicular pathway is evidently more important in the mechanism of formation of OKN that of RPN.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 62, No. 2, pp. 196–200, February, 1976.     

Motion sensitivity in cat's superior colliculus: contribution of different visual processing channels to response properties of collicular neurons

It is well established that neurons in the retinorecipient layers of superior colliculus (SC), the mammalian homologue of the optic tectum of other vertebrates, are extremely sensitive to moving stimuli. In our studies we have distinguished several functionally distinct groups of neurons in the retinorecipient layers of the SC of the cat on the basis of their velocity response profiles. Our data revealed substantial convergence of the Y and non-Y information channels on single SC neurons. Second, using the method of selective conduction block of the Y-type fibers in one optic nerve we have shown that responses of SC cells to high-velocity motion are dependant on the integrity of Y-type input. Third, in order to determine the degree of influence of the X- and W-type input on cellular responses we have examined spatial and temporal frequency response profiles of single collicular neurons using sinusoidal gratings drifting in the preferred direction. At any given eccentricity, most collicular neurons exhibited a preference for relatively very low spatial frequencies. The preference for low spatial frequencies combined with temporal frequency profiles of collicular neurons suggests that the Y- and W-type inputs constitute the major functional inputs to the retinorecipient layers of the SC and that the "top-down" X-type input from the visual cortex has only a minor impact on the spatio-temporal frequency response profiles of collicular receptive fields.     

Contralateral cortical projections to the superior colliculus in the macaque monkey

Summary Cortical projections from the contralateral hemisphere to the superior colliculus (SC) were studied in macaque monkey using retrograde transport of the enzyme horseradish peroxidase (HRP). After single or multiple injections of HRP into SC, labelled cells were found contralaterally in layer V of the anterior bank of the arcuate sulcus, the origin of this contralateral projection being confined to the anterior part of Brodmann's area 6. Only a few labelled cells appeared in adjacent area 8. Labelled cells occured in patches, forming bands which were found to run in a ventromedial direction. A similar pattern was seen homotopically in ipsilateral area 6. Thus, this anterior part of area 6 gives rise to a bilateral projection to the SC. The findings emphasize structural differences in a region of the frontal lobe which has been considered functionally uniform as frontal eye field.Supported by Deutsche Forschungsgemeinschaft (SFB 50/C6 and Di 212/2)     

Comparison of saccades perturbed by stimulation of the rostral superior colliculus, the caudal superior colliculus, and the omnipause neuron region

Over the past decade, considerable research efforts have been focused on the role of the rostral superior colliculus (SC) in control of saccades. The most recent theory separates the deeper intermediate layers of the SC into two functional regions: the rostral pole of these layers constitutes a fixation zone and the caudal region comprises the saccade zone. Sustained activity of fixation neurons in the fixation zone is argued to maintain fixation and help prevent saccade generation by exciting the omnipause neurons (OPNs) in the brain stem. This hypothesis is in contrast to the traditional view that the SC contains a topographic representation of the saccade motor map on which the rostral pole of the SC encodes signals for generating small saccades (<2 degrees ) instead of preventing them. There is therefore an unresolved controversy about the specific role on the most rostral region of the SC, and we reexamined its functional contribution by quantifying and comparing spatial and temporal trajectories of 30 degrees saccades perturbed by electrical stimulation of the rostral pole and more caudal regions in the SC and of the OPN region. If the rostral pole serves to preserve fixation, then saccades perturbed by stimulation should closely resemble interrupted saccades produced by stimulation of the OPN region. If it also contributes to saccade generation, then the disrupted movements would better compare with redirected saccades observed after stimulation of the caudal SC. Our experiments revealed two significant findings: 1) the locus of stimulation was the primary factor determining the perturbation effect. If the directions of the target-directed saccade and stimulation-evoked saccade were aligned and if the stimulation was delivered within approximately the rostral 2 mm (<10 degrees amplitude) of SC, the ongoing saccade stopped in midflight but then resumed after stimulation end to reach the original visually specified goal with close to normal accuracy. When stimulation was applied at more caudal sites, the ongoing saccade directly reached the target location without stopping at an intermediate position. If the directions differed considerably, both initial and resumed components were typically observed for all stimulation sites. 2) A quantitative analysis of the saccades perturbed from the fixation zone showed significant deviations from their control spatial trajectories. Thus they resembled redirected saccades induced by caudal SC stimulation and differed significantly from interrupted saccades produced by OPN stimulation. The amplitude of the initial saccade, latency of perturbation, and spatial redirection were greatest for the most caudal sites and decreased gradually for rostral sites. For stimulation sites within the rostral pole of SC, the measures formed a smooth continuation of the trends observed in the saccade zone. As these results argue for the saccade zone concept, we offer reinterpretations of the data used to support the fixation zone model. However, we also discuss scenarios that do not allow an outright rejection of the fixation zone hypothesis.     

Projections from auditory structures to the superior colliculus in the rat

Arginine-vasopressin (AVP) and related peptides were administered by microinjection into the nucleus tractus solitarius of the rat. AVP produced a rise both in mean arterial pressure and in heart rate. This effect was abolished by pretreatment with a specific antagonist of V1 receptors and was not seen either after injections of oxytocin or of the V2 agonist deamino-D-arginine-vasopressin. This study provides evidence for a specific action of vasopressin on the cardiovascular system in the nucleus of the tractus solitarius, which is mediated neither by V2 nor oxytocin receptors.