Recent Saccadic Eye Movement Research Uncovers Patterns of Cognitive Dysfunction in Schizophrenia.

The frontal cortex and the subcortical areas of the brain play a major role in the control of thought and action. Eye movements are increasingly used in neuropsychological research to explore the executive and sensorimotor functions of such neural networks. This interface links the control of action, at the fundamental levels of neurophysiological and neurochemical processes, with the high-level cognitive operations that underlie visual orienting. Patients with schizophrenia have neurocognitive impairments that can be readily investigated with novel saccadic eye movement paradigms. Animal, human lesion, and neuroimaging studies have identified the cerebral centers that underlie saccadic eye movements. The areas of the prefrontal cortex include the dorsolateral prefrontal cortex, the frontal eye fields, the supplementary eye fields, and the anterior cingulate gyrus. Pathology of saccadic eye movements therefore provides information on the functional status of the underlying neural circuitry in brain disorders such as schizophrenia

The plasticity of human saccadic eye movements

The central purpose of this research has been to examine the possibility of the plasticity of individual saccadic parameters and to identify their patterns of covariation. Experiments using trial-by-trial feedback or continuous on-going feedback methods demonstrated that the saccadic generator can prolong the duration of a saccade above normal levels. However, slowed peak velocities were only evident with continuous feedback. The results showed that although continuous feedback was a more effective method for inducing modifications of saccade trajectories, the effects of trial-by-trial feedback schedules were enhanced by distributing the training over several days. The instructions to produce slow saccades caused a 'staircase' pattern of eye movements in which a continuous sequence of hypometric saccades was manifested. These saccades had latencies 400-600 msecs longer than normal visually controlled eye movements. Detailed measurements (chapter 4) of the latencies of the saccadic components indicated that each component was programmed independently. In chapter 5 the Gurevich claim that a saccade velocity depends only on the spatial magnitude of the saccade was tested by measuring saccades of equivalent amplitudes to targets which varied in movement duration and velocity. The accuracy of saccades but not their peak velocities or durations was sensitive to manipulations in the temporal characteristics of the target. Experiments in chapter 6 showed that the use of spatial signals in the aiming of a saccade can be systematically controlled. When subjects were trained for several days in a visual discrimination task the accuracy of the initial saccadic movement increased over time. The results of these experiments seriously question the Young and Stark (1963b) ballistic model and other formulations (Westheimer, 1954b, 1973; Yarbus, 1967) which assume that the saccadic system operates according to stereotyped mechanisms

Distinguishing between impairments of working memory and inhibitory control in cases of early dementia

Dementia (most notably, Alzheimer’s Disease) is often associated with impairments of both working memory and inhibitory control. However, it is unclear whether these are functionally distinct impairments. We addressed the issue of whether working memory and inhibitory control can be dissociated, using data from a sample of patients who were recruited in a longitudinal study (Crawford et al. 2013, 2015). The first case revealed a preserved working memory capacity together with poor inhibitory control in the anti-saccade task. A longitudinal follow-up revealed that the defective inhibitory control emerged 12-months before the dementia was evident on the mini-mental state examination assessment. A second case revealed a poor working memory together with a well-preserved level of inhibitory control. The dissociation of working memory and inhibitory control was confirmed statistically in 7 additional cases. These findings yield converging evidence that working memory and inhibitory control are distinct cognitive operations and challenges the Kimberg and Farah (2000) cognitive model of working memory

The role of motivation, glucose and self-control in the antisaccade task

Research shows that self-control is resource limited and there is a gradual weakening in consecutive self-control task performance akin to muscle fatigue. A body of evidence suggests that the resource is glucose and consuming glucose reduces this effect. This study examined the effect of glucose on performance in the antisaccade task - which requires self-control through generating a voluntary eye movement away from a target - following self-control exertion in the Stroop task. The effects of motivation and individual differences in self-control were also explored. In a double-blind design, 67 young healthy adults received a 25g glucose or inert placebo drink. Glucose did not enhance antisaccade performance following self-control exertion in the Stroop task. Motivation however, predicted performance on the antisaccade task; more specifically high motivation ameliorated performance decrements observed after initial self-control exertion. In addition, individuals with high levels of self-control performed better on certain aspects of the antisaccade task after administration of a glucose drink. The results of this study suggest that the antisaccade task might be a powerful paradigm, which could be used as a more objective measure of self-control. Moreover, the results indicate that level of motivation and individual differences in self-control should be taken into account when investigating deficiencies in self-control following prior exertion

Eye Movement Latency Coefficient of Variation as a Predictor of Cognitive Impairment:An Eye Tracking Study of Cognitive Impairment

Studies have demonstrated impairment in the control of saccadic eye movements in Alzheimer’s disease (AD) and people with mild cognitive impairment (MCI) when conducting the pro-saccade and antisaccade tasks. Research has shown that changes in the pro and antisaccade latencies may be particularly sensitive to dementia and general executive functioning. These tasks show poten-tial for diagnostic use as they provide a rich set of potential eye-tracking markers. One such marker, the coefficient of variation (CV), has so far been overlooked. For biological markers to be reliable they must be able to detect abnormalities in preclinical stages. MCI is often viewed as a predecessor to AD with certain classifications of MCI more likely than others to progress to AD. The current study examined the potential of CV scores on pro and antisaccade tasks to distin-guish participants with AD, amnestic MCI (aMCI), non-amnesiac MCI (naMCI) and older con-trols. The analyses revealed no significant differences in CV scores across the groups using the pro or antisaccade task. Antisaccade mean latencies were able to distinguish participants with AD and the MCI subgroups. Future research is needed into CV measures and attentional fluctuations in AD and MCI individuals to fully assess this measures potential to robustly distinguish clinical groups with high sensitivity and specificity

Active Visual Inhibition is Preserved in the Presence of a Distracter:A Cross-cultural, Ageing and Dementia Study

The current study investigated a novel visual distracter task as a potential diagnostic marker for the detection of cognitive impairment and the extent to which this compares in healthy ageing across two cultures. The Inhibition of a Recent Distracter Effect (IRD) refers to the inhibition of a saccadic eye movement towards a target that is presented at the location of a previous distracter. The current study compared the IRD across a large cross-cultural sample comprising of young (N=75), old European participants (N=119), old south Asian participants (N=83), participants with Dementia due to Alzheimer’s disease (N=65) and Mild cognitive impairment (N=91). Significantly longer saccadic reaction times on the target to distracter trials, in comparison to the target to target trials were evident in all groups and age cohorts. Importantly, the IRD was also preserved in participants with Alzheimer’s Disease and mild cognitive impairment demonstrating that the IRD is robust across cultures, age groups and clinical populations. Eye-tracking is increasingly used as a dual diagnostic and experimental probe for the investigation of cognitive control in Alzheimer’s disease. As a promising methodology for the early diagnosis of dementia, it is important to understand the cognitive operations in relation to eye-tracking that are well preserved as well as those that are abnormal. Paradigms should also be validated across ethnicity/culture, clinical groups and age cohorts

On the Effect of Bilateral Eye Movements on Memory Retrieval in Ageing and Dementia

It has been reported that performing bilateral eye movements for a short period can lead to an enhancement of memory retrieval and recall (termed the “saccade induced retrieval effect (SIRE)”). The source of this effect has been debated within the literature and the phenomenon has come under scrutiny as the robustness of the effect has recently been questioned. To date investigations of SIRE have largely been restricted to younger adult populations. Here, across two experiments, we assess the robustness and generalisability of the SIRE specifically in relation to disease and ageing. Experiment 1 employed a between subject’s design and presented younger and older participants with 36 words prior to completing one of three eye movement conditions (bilateral, antisaccade or a fixation eye movement). Participants then performed a word recognition task. Experiment 2 assessed the SIRE in individuals diagnosed with Alzheimer’s, Mild cognitive impairment and Parkinson’s by employing an online within subject’s design. Results showed no significant difference between groups in the number of words recognised based on eye movement condition. Neither experiment 1 or 2 replicated the SIRE effect therefore the findings from this study add to the growing number of studies that have failed to replicate the SIRE effect

A third-person perspective on co-speech action gestures in Parkinson's disease

A combination of impaired motor and cognitive function in Parkinson’s disease (PD) can impact on language and communication, with patients exhibiting a particular difficulty processing action verbs. Co-speech gestures embody a link between action and language and contribute significantly to communication in healthy people. Here, we investigated how co-speech gestures depicting actions are affected in PD, in particular with respect to the visual perspective—or the viewpoint – they depict. Gestures are closely related to mental imagery and motor simulations, but people with PD may be impaired in the way they simulate actions from a first-person perspective and may compensate for this by relying more on third-person visual features. We analysed the action-depicting gestures produced by mild-moderate PD patients and age-matched controls on an action description task and examined the relationship between gesture-viewpoint, action-naming, and performance on an action observation task (weight judgement). Healthy controls produced the majority of their action-gestures from a first person perspective, whereas PD patients produced a greater proportion of gestures produced from a third person perspective. We propose that this reflects a compensatory reliance on third-person visual features in the simulation of actions in PD. Performance was also impaired in action-naming and weight judgement, although this was unrelated to gesture viewpoint. Our findings provide a more comprehensive understanding of how action-language impairments in PD impact on action communication, on the cognitive underpinnings of this impairment, as well as elucidating the role of action simulation in gesture production

The influence of Schizotypy on Event Related Oscillations in Sensory Gating during early Infant Development

Maternal personality is known to influence childhood risk factors for mental health. More specifically, maternal psychopathologies, such as those on the schizophrenia-spectrum have been associated with P50 sensory gating abilities. Schizotypy is a personality dimension within the general population elevated among schizophrenia-spectrum patients and their first-degree relatives. Sensory gating is the pre-attentional habituation of responses distinguishing between important and irrelevant information. Neurooscillatory deficits have been observed in this ability in individuals diagnosed with schizophrenia. The current study investigated whether mothers with schizotypy (n=33) and their 6-month-old infants (n=38) display reduced evoked-oscillatory activity. The mothers completed the Oxford-Liverpool Inventory of Feelings and Experiences – Short Form as an index of schizotypy dimensionality, which was used to categorise the participants into infants of control mothers and mothers with schizotypy. The paired-tone paradigm: two identical auditory tones (Stimulus 1 and Stimulus 2) played 500ms apart, were used to probe evoked oscillatory activity. Data revealed that although the infants’ evoked-oscillations displayed differences between Stimulus 1 and Stimulus 2, there were no group differences between infants of mothers with schizotypy and of control mothers. Their mothers, however, displayed differences, with reduced power toward Stimulus 1 observed in the mothers with schizotypy between 13-30Hz. These findings are consistent that early sensory processes, such as sensory gating are impaired in schizophrenia-spectrum disorders

Memory-Guided Saccades in Psychosis: Effects of Medication and Stimulus Location.

The memory-guided saccade task requires the remembrance of a peripheral target location, whilst inhibiting the urge to make a saccade ahead of an auditory cue. The literature has explored the endophenotypic deficits associated with differences in target laterality, but less is known about target amplitude. The data presented came from Crawford et al. (1995), employing a memory-guided saccade task among neuroleptically medicated and non-medicated patients with schizophrenia (n = 31, n = 12), neuroleptically medicated and non-medicated bipolar affective disorder (n = 12, n = 17), and neurotypical controls (n = 30). The current analyses explore the relationships between memory-guided saccades toward targets with different eccentricities (7.5° and 15°), the discernible behaviour exhibited amongst diagnostic groups, and cohorts distinguished based on psychotic symptomatology. Saccade gain control and final eye position were reduced among medicated-schizophrenia patients. These metrics were reduced further among targets with greater amplitudes (15°), indicating greater deficit. The medicated cohort exhibited reduced gain control and final eye positions in both amplitudes compared to the non-medicated cohort, with deficits markedly observed for the furthest targets. No group differences in symptomatology (positive and negative) were reported, however, a greater deficit was observed toward the larger amplitude. This suggests that within the memory-guided saccade paradigm, diagnostic classification is more prominent in characterising disparities in saccade performance than symptomatology