Involuntary saccades and binocular coordination during visual pursuit in Parkinson's disease

Prior studies of oculomotor function in Parkinson's disease (PD) have either focused on saccades while smooth pursuit eye movements were not involved, or tested smooth pursuit without considering the effect of any involuntary saccades. The present study investigated whether these involuntary saccades could serve as a useful biomarker for PD. Ten observers with PD participated in the study along with 10 age-matched normal control (NC) and 10 young control participants (YC). Observers fixated on a central cross while a disk (target) moved toward it from either side of the screen. Once the target reached the fixation cross, observers began to pursue the moving target until the target reached to the other side. To vary the difficulty of fixation and pursuit, the moving target was presented on a blank or a moving background. The moving background consisted of uniformly distributed dots moved in either the same or the opposite direction of the target once the target reached the central fixation cross. To investigate binocular coordination, each background condition was presented under a binocular condition, in which both eyes saw the same stimulus, and under a dichoptic condition, in which one eye saw only the target and the other eye only saw the background. The results showed that in both background conditions, observers with PD made more involuntary saccades than NC and YC during both fixation and pursuit periods while YC and NC showed no difference. Moreover, the difference between left and right eye positions increased over time during the pursuit period for PD group but not for the other two groups. This suggests that individuals with PD may be impaired not only in saccade inhibition, but also in binocular coordination during pursuit. [Meeting abstract presented at VSS 2016.]Accepted manuscrip

Numerical Cognition and Autism Spectrum Traits in Adults

Evidence suggests that individuals with high-functioning autism spectrum disorder (ASD) may be particularly inclined toward math proficiency, especially in adulthood. There is also evidence, however, that many of those with an ASD struggle in math as children compared to their typically-developing peers. These ostensibly inconsistent findings may indicate that individuals with an ASD struggle with number sense, a precursor to formal math, rather than with formal math per se. This account is compatible with evidence of a specific form of neural dysregulation, excitatory/inhibitory imbalance, in ASD that results in reduced signal-to-noise ratios (SNR) for processes that occur in downstream neural regions (such as association cortex). Based on this view, formal math, a task with enhanced SNR due to standardization, would likely be intact for individuals with an ASD, while number sense, a domain localized to association cortex that lacks SNR enhancement via standardization, would take longer to sufficiently refine and would delay formal math acquisition for this population. The current studies examined whether a neural dysregulation account of ASD effectively predicts and explains numerical cognition performance across ASD traits. Experiment 1 examined whether scores on the Autism-Spectrum Quotient and the Systemizing Quotient predict performance on measures of numerical cognition consistent with a neural dysregulation account and in contrast to a traditional hyper-systemizing account of ASD. Experiment 2 examined whether strengthening the stimulus signal by presenting stimuli multimodally improves number sense performance across the range of ASD traits, as well as whether manipulation of high-level stimulus features affects multisensory integration in a manner consistent with a neural dysregulation account

Top-down modulation and memory deficits: Neural enhancement in the context of aging

Top-down modulation from a broader perspective suggests that some effortful control over posterior brain regions occurs. This study examined the extent to which age-related differences in top-down modulation could explain age-related memory decline. The theory of top-down modulation suggests that neural transmission during encoding requires the enhancement of relevant information and suppression of irrelevant information for efficacious neural function. Enhancement of attention to stimuli should be greater under higher task demands. In this study, we compared cortical modulation in a less effortful facial encoding task to cortical modulation in a more effortful facial encoding task. One-hundred-thirty older adults (mean age = 66.43 yrs) and 30 younger adults (mean age = 24.13 yrs) completed 2 tasks of facial encoding using functional magnetic resonance imaging (fMRI), a structural magnetic resonance imaging (MRI) scan, and a computer administered test of facial recognition outside the scanning environment. Activity in the fusiform face area was extracted when participants were told to view faces in the first encoding task and remember faces in the second encoding task. An enhancement index reflected the change in neural activity in the fusiform face area moving from the view faces task to the remember faces task. As predicted, levels of neural enhancement in the fusiform face area significantly predicted older and younger adult participants’ ability to correctly discriminate between faces they had and had not previously seen. Against predictions, the level of fusiform face area enhancement did not differ between younger and older adults. Thus, differences in enhancement levels are not driving age-related differences in facial recognition discrimination ability. In functional connectivity analysis, the idea that connections between the “top” and “bottom” components of the memory encoding network were examined. Consistent with predictions, the functional connection between right ventrolateral prefrontal cortex and the fusiform face area related with recognition. Taken together these data suggest that sensory enhancement is a critical component of efficacious memory encoding processes, but top-down enhancement of sensory activity does not adequately explain age-related decrement in memory performance

Visual System Development in People with One Eye: Behaviour and Structural Neural Correlates

Postnatal monocular deprivation from the surgical removal (enucleation) of one eye in humans results in intact spatial form vision, although its consequences on motion perception development are less clear. Changes in brain structure following early monocular enucleation have either been assessed in species whose visual system is quite different from humans, or in enucleated monkeys and humans following short-term survival. In this dissertation, I sought to determine the long-term effects of enucleation on visual system development by examining behavioural visual abilities and visual system morphology in adults who have had one eye enucleated early in life due to retinoblastoma. In Chapter II, I conducted a series of speed and luminance contrast discrimination tasks not yet implemented in this group. Early monocular enucleation results in impaired speed discrimination but intact contrast perception compared to binocular and monocular viewing controls. These findings suggest differential effects of enucleation on the development of spatial form vision and motion perception. In Chapters III and IV, I obtained high-resolution structural magnetic resonance images to assess the morphological development of subcortical (Chapter III) and cortical (Chapter IV) structures in the visual pathway. Early monocular enucleation resulted in decreased optic chiasm width and volume, optic tract diameters, and lateral geniculate nuclei (LGN) volumes compared with binocularly intact controls. Surprisingly, however, optic tract diameter and LGN volume decreases were less severe contralateral to the remaining eye. Early monocular enucleation also resulted in increased grey matter surface area of visual and non-visual cortices compared with binocularly intact controls. Consistent with the LGN asymmetry, increased surface area of the primary visual cortex was restricted to the hemisphere contralateral to the remaining eye. Surprisingly, however, these increases were found for those with right- but not left-eye enucleation, suggesting different developmental time periods for each hemisphere. Possible mechanisms of altered development following early monocular enucleation include: 1) recruitment of deafferented cells by the remaining eye, 2) retention of deafferented cells due to feedback from visual cortex, and 3) a disruption in synaptic pruning. These data highlight the importance of receiving normal levels of binocular visual input during infancy for typical visual development

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Auditory critical periods: A review from system’s perspective

AbstractThe article reviews evidence for sensitive periods in the sensory systems and considers their neuronal mechanisms from the viewpoint of the system’s neuroscience. It reviews the essential cortical developmental steps and shows its dependence on experience. It differentiates feature representation and object representation and their neuronal mechanisms. The most important developmental effect of experience is considered to be the transformation of a naive cortical neuronal network into a network capable of categorization, by that establishing auditory objects. The control mechanisms of juvenile and adult plasticity are further discussed. Total absence of hearing experience prevents the patterning of the naive auditory system with subsequent extensive consequences on the auditory function. Additional to developmental changes in synaptic plasticity, other brain functions like corticocortical interareal couplings are also influenced by deprivation. Experiments with deaf auditory systems reveal several integrative effects of deafness and their reversibility with experience. Additional to developmental molecular effects on synaptic plasticity, a combination of several integrative effects of deprivation on brain functions, including feature representation (affecting the starting point for learning), categorization function, top–down interactions and cross-modal reorganization close the sensitive periods and may contribute to their critical nature. Further, non-auditory effects of auditory deprivation are discussed. To reopen critical periods, removal of molecular breaks in synaptic plasticity and focused training therapy on the integrative effects are required

Cannabis Use and Affective Processing: a Brain Structure Analysis

Cannabis is the most commonly used illicit drug amongst adolescents and young adults in the United States. Previously, cannabis and its components have been associated with differences in affective processing and neural functioning. Participants (ages 16-25) were cannabis users and non-users excluded for psychiatric disorders, major medical conditions, and excessive other drug use. A series of multiple regressions examined whether past year cannabis use and cannabis x gender predicted measures of emotional face processing (using the PennCNP affective battery) as well as volumes in bilateral prefrontal, temporal, limbic, and cerebellar regions, as well as frontolimbic white matter tracts. Subsequently, Pearson correlations were conducted within the cannabis group to assess whether brain regions significantly associated with cannabis use predicted mood and affective processing. Increased cannabis use was associated with higher Acuity Neutral scores, smaller left rostral anterior cingulate (rACC) volumes, larger superior temporal volumes, and reduced right uncinate fasciculus mean diffusivity. Significant cannabis x gender interactions were observed for left rACC and forceps minor fractional anisotropy (FA). Greater cannabis use was associated with smaller left rACC volumes only within females, as well as greater forceps minor FA in females and reduced FA in males. Within the cannabis-using group, smaller rACC volumes were correlated with lower Emotion Discrimination Correct scores. These findings suggest that cannabis use exerts dose dependent effects on frontolimbic circuitry, which are in turn associated with deficits in affective processing. This may be one potential mechanism underlying high comorbidity rates between chronic cannabis use and psychiatric disorders

Differences between the sexes in sensory sensitivity and performance in the visual and auditory modalities

50 young adult males and 50 females undertook a series of psychophysical experiments in the auditory and visual modalities, testing (i) sensory threshold, (H) the subjective response to intensity,· and (Hi) discriminatory ability (the Phase 1 experiments). Significant differences between the sexes in performance in the auditory modality were found in absolute threshold for some frequencies with females being more sensitive in each instance. In their subjective response to intensity in the auditory modality, females consistently set levels 8 - 9 dB lower than those set by males at all frequencies. In all instances the difference was statistically significant. No significant differences between the sexes were obtained in their ability to discriminate pitch. In the visual modality significant differences between the sexes are not apparent for dark adaptation (used as a test of threshold) or the subjective reaction to intensity (glare). Analysis of the visual acuity scores (discriminatory ability) shows a sex difference in favour of the males (p> 0.01). Extensive correlational analyses are employed to examine within-mode and inter-modality relationships. The lack of consistent significant and high relationships obtained indicate that sensory sensitivity is not a consistent property of the nervous system, and presents some problems for current theories of personality. The effects of the menstrual cycle on female performance in the auditory and visual modality tasks are also considered, and the data indicates that hormonal influences are implicated. Having established that some differences between the sexes do exist in the performance of visual and auditory tasks at the sensory or basic perceptual levels, the second phase experiments (administering the Bennett Differential Aptitude Tests) were commenced. The rationale and methodology for these experiments is described. Significant differences between the male and female groups in this study were not apparent in any of the Verbal/Language Usage tests, but significant differences in favour of the males were obtained for Space Relations (p.> 0.05) and Mechanical Reasoning (p>0.02). Correlational analyses between the auditory and visual parameters and the cognitive abilities tested on the. Bennett DAT showed high significant relationships (p > 0 .01) between auditory intensity tolerance and all the Verbal/Language Usage tests, and a significant relationship for the total sample (p >0·.05) between visual acuity and the Space Relations test. The implications of the data obtained in this study for existing theories of sex differences are discussed

A Study in the Comparison of Ocular and Extremity Dominance Among a Stuttering and Non-Stuttering School-Age Population

The nul-hypothesis has been confirmed by the analysis of the study, in that they show no relationship between stuttering and unilateral dominance. The results indicate that the laterality measure of the experimental group did not differ significantly from that of the control group. In as much as the results of only one statistical test were significant, it is felt that this does not detract from the contribution of the study. It would seem that the results obtained from this comparison, the analysis of overall visual adequacy and extremity dominance, could have occurred by chance alone. It is pointed out, however, that this test was distinctly different from all other tests performed; and it is felt that careful consideration should he given to this factor in a total evaluation of the results obtained. The statistical analysis of the data compiled were done by way of the. t\u27 test of significance, which included computation of the t\u27 statistic to test whether scores obtained on selected tests were statistically significant, and the Chi Square Test, which was used to determine the presence or absence of factors indicating a greater or less degree of dominance confusion. The experimental and control groups were composed of a total of twenty subjects, who were administered The Harris Tests of Lateral Dominance, the Leavell Hand-Eye Coordinator Tests, and the Keystone Visual Survey; Tests for the purpose of exploring the relationship of measures of lateral dominance. On the basis of the results obtained from this investigation, the following conclusions seem warranted: Stuttering subjects do not show a higher incidence of extremity and ocular dominance confusion that do non-stuttering controls. The lack of unilateral dominance would not be considered a factor regarding lateral dominance as it relates to stuttering. A significantly greater proportion of stutterers were shown to have a visual inadequacy in association with extremity in-coordination and imbalance. Further research of the relationship of lateral dominance confusion and stuttering observed by more clinicians is needed. Further research in the development of instruments to assess lateral dominance is indicated. [Keywords: Stuttering, Neurological Organization, Lateral Dominance, Mixed Dominance, Dominant Eye