Biology subjects

Thompson, B.

Publications and source records attributed to Thompson, B..

27 records · Page 2Linked to original sources

bioRxiv2019

Early life maturation of human visual system white matter is altered by monocular enucleation

Monocular enucleation early in life and the resultant lack of binocular visual input during visual development results in functional and structural brain changes in adulthood, including alterations in white matter microstructure. However, the time courses of these neurodevelopmental changes are unknown. Here, we investigated whether structural brain changes were present at 8 to 12 years of age in a group of children with a history of monocular enucleation prior to 3 years of age (the ME group) relative to control participants with normal binocular vision (the BC group). Structural connectivity was measured using diffusion tensor imaging (DTI). Relative to the BC group, the ME group exhibited significantly increased radial and mean diffusivity in the optic radiation contralateral to the enucleated eye, the bidirectional interhemispheric V1 to V1 tracts and the V1 to MT tract ipsilateral to the enucleated eye. These changes indicate abnormal myelinization and reduced axonal density in subcortical and cortical visual pathway white matter structures following unilateral enucleation and loss of binocular vision. Our findings are broadly consistent with those recently reported for older uniocular individuals suggesting that these effects are present in childhood and persist into adulthood.

neuroscience↗

bioRxiv2019

Multi-session visual cortex transcranial random noise stimulation in adults with amblyopia

PurposeWe tested the hypothesis that five daily sessions of visual cortex transcranial random noise stimulation would improve contrast sensitivity, crowded and uncrowded visual acuity in adults with amblyopia. MethodsNineteen adults with amblyopia (44.2 {+/-} 14.9yrs, 10 female) were randomly allocated to active or sham tRNS of the visual cortex (active, n = 9; sham, n = 10). tRNS was delivered for 25 minutes across five consecutive days. Monocular contrast sensitivity, uncrowded and crowded visual acuity were measured before, during, 5 minutes and 30 minutes post stimulation on each day. ResultsActive tRNS significantly improved contrast sensitivity and uncrowded visual acuity for both amblyopic and fellow eyes whereas sham stimulation had no effect. An analysis of the day by day effects revealed large within session improvements on day 1 for the active group that waned across subsequent days. No long-lasting (multi-day) improvements were observed for contrast sensitivity, however a long-lasting improvement in amblyopic eye uncrowded visual acuity was observed for the active group. This improvement remained at 28 day follow up. However, between-group differences in baseline uncrowded visual acuity complicate the interpretation of this effect. No effect of tRNS was observed for amblyopic eye crowded visual acuity. ConclusionsIn agreement with previous non-invasive brain stimulation studies using different techniques, tRNS induced short-term contrast sensitivity improvements in adult amblyopic eyes, however, multiple sessions of tRNS did not lead to enhanced or long-lasting effects for the majority of outcome measures.

neuroscience↗

bioRxiv2019

Ultraviolet radiation exposure and melanoma: evidence for gene-environment interaction in a large prospective cohort

Melanoma develops as the result of complex interactions between sun exposure and genetic factors. Data on the relationship between sunlight and melanoma from prospective studies are scant, and the combination of ultraviolet exposure data collected before melanoma diagnosis and genetic information is rarer still. We aimed to quantify the association between ambient and personal UV exposure in relation to risk of incident melanoma (invasive; invasive+in situ) in a large population-based prospective study of men and women (n=38,833) residing in a high ambient UV setting, and to examine potential gene-environment interactions. During a median follow-up time of 4.4 years, 782 (1.5%) participants developed cutaneous melanoma (316 invasive, 466 in situ). Country of birth, age at migration and sunburns during all periods of life were significantly associated with melanoma risk. Histories of keratinocyte cancer and of other actinic lesions were both strongly associated with melanoma risk. An interaction with polygenic risk is possible; among people at low risk, markers of cumulative sun exposure were associated with melanoma. In contrast, among people at high polygenic risk, markers of high-level early life ambient exposure were associated with melanoma. Polygenic risk scores can assist in identifying individuals for whom sunlight exposure is most relevant.

epidemiology↗

bioRxiv2019

Is asthma associated with exposure to smoke from a coal mine fire?

In 2014, a fire at the Hazelwood open cut coal mine (Victoria, Australia) burned for about 6 weeks. Residents of the adjacent town of Morwell were exposed to high levels of fine particulate matter (PM2.5) during this period. Three and a half years after the event, this study aimed to investigate the long-term impact of short-term exposure to coal mine fire smoke on asthma.\n\nA cross-sectional analysis was undertaken on a group of exposed participants with asthma from Morwell (n=165) and a group of unexposed participants with asthma from the control town of Sale (n=64). Town exposure status was determined by modelled PM2.5 data for the mine fire period. Respiratory symptoms were assessed with a validated respiratory health questionnaire and symptom severity score. Asthma control was assessed with an asthma control questionnaire. Lung function testing included spirometry, bronchodilator response, and fraction of exhaled nitric oxide.\n\nThere was no evidence that exposed Morwell participants had more severe asthma symptoms, worse lung function, or more eosinophilic airway inflammation compared to unexposed Sale participants. However there was some evidence that Morwell participants had more uncontrolled than well-controlled asthma, compared to the participants from Sale (adjusted relative risk ratio 2.71 95%CI: 1.02, 7.21, p=0.046).\n\nThree and a half years after exposure, coal mine fire smoke does not appear to be associated with more severe asthma symptoms or worse lung function, but may be associated with poorer asthma control.\n\nSummary take home messageIn people with asthma, short-term coal mine fire smoke exposure does not appear to have long-term impact on severity of asthma symptoms, lung function or eosinophilic airway inflammation, but may affect asthma control.

epidemiology↗

bioRxiv2019

Continuous theta burst TMS of area MT+ impairs attentive motiontracking.

Attentive motion tracking deficits, measured using multiple object tracking (MOT) tasks, have been identified in a number of visual and neurodevelopmental disorders such as amblyopia and autism. These deficits are often attributed to the abnormal development of high-level attentional networks. However, neuroimaging evidence from amblyopia suggests that reduced MOT performance can be explained by impaired function in motion sensitive area MT+ alone. To test the hypothesis that MT+ plays an important role in MOT, we assessed whether modulation of MT+ activity using continuous theta burst stimulation (cTBS) influenced MOT performance in participants with normal vision. An additional experiment involving numerosity judgements of MOT stimulus elements was conducted to control for non-specific effects of MT+ cTBS on psychophysical task performance. The MOT stimulus consisted of 4 target and 4 distractor dots and was presented at 10{degrees} eccentricity in the right or left hemifield. Functional MRI-guided cTBS was applied to left MT+. Participants (n = 13, age:27 {+/-} 3) attended separate active and sham cTBS sessions where the MOT task was completed before, 5 mins post and 30 mins post cTBS. Active cTBS significantly impaired MOT task accuracy relative to baseline for the right (stimulated) hemifield 5 mins (10 {+/-} 2% reduction; t12 = 1.95, p = 0.03) and 30 mins (14 {+/-} 3% reduction; t12 = 2.96, p = 0.01) post stimulation. No impairment occurred within the left (control) hemifield after active cTBS or for either hemifield after sham cTBS. Numerosity task performance was unaffected by cTBS. These results highlight the importance of lower-level motion processing for MOT and suggest that abnormal function of MT+ alone is sufficient to cause a deficit in MOT task performance.

neuroscience↗

bioRxiv2019

The effect of combined patching and citalopram on visual acuity in adults with amblyopia: a randomized, crossover, placebo-controlled trial

Non-human animal models have demonstrated that selective serotonin reuptake inhibitors (SSRIs) can enhance plasticity within the mature visual cortex and enable recovery from amblyopia. The aim of this study was to test the hypothesis that the SSRI citalopram combined with part-time patching of the fellow fixing eye would improve amblyopic eye visual acuity in adult humans. Following a cross-over, randomized, double blind, placebo-controlled design (pre-registration: ACTRN12611000669998), participants completed two 2-week blocks of fellow fixing eye patching. One block combined patching with citalopram (20 mg/day) and the other with a placebo tablet. The blocks were separated by a 2-week washout period. The primary outcome was change in amblyopic eye visual acuity. Secondary outcomes included stereoacuity and electrophysiological measures of retinal and cortical function. Seven participants were randomized, fewer than our pre-specified sample size of 20. There were no statistically significant differences in amblyopic eye visual acuity change between the active (mean {+/-} SD change = 0.08{+/-}0.16 logMAR) and the placebo (mean change = -0.01{+/-}0.03 logMAR) blocks. No treatment effects were observed for any secondary outcomes. However, 3 of 7 participants experienced a 0.1 logMAR or greater improvement in amblyopic eye visual acuity in the active but not the placebo block. These results from a small sample suggest that larger-scale trials of SSRI treatment for adult amblyopia may be warranted. Considerations for future trials include drug dose, treatment duration and recruitment challenges.

clinical trials↗

bioRxiv2019

Anodal transcranial direct current stimulation reduces collinear lateral inhibition in normal peripheral vision

Collinear flanking stimuli can reduce the detectability of a Gabor target presented in peripheral vision. This phenomenon is called collinear lateral inhibition and it may contribute to crowding in peripheral vision. Perceptual learning can reduce collinear lateral inhibition in peripheral vision, however intensive training is required. Our aim was to assess whether modulation of collinear lateral inhibition can be achieved within a short time-frame using a single 20-minute session of primary visual cortex anodal transcranial direct current stimulation (a-tDCS). Thirteen observers with normal vision performed a 2AFC contrast detection task with collinear flankers positioned at a distance of 2{lambda} from the target (lateral inhibition) or 6{lambda} (control condition). The stimuli were presented 6{degrees} to the left of a central cross and fixation was monitored with an infra-red eye tracker. Participants each completed two randomly sequenced, single-masked stimulation sessions; real anodal tDCS and sham tDCS. For the 2{lambda} separation condition, a-tDCS induced a significant reduction in detection threshold (reduced lateral inhibition). Sham stimulation had no effect. No effects of a-tDCS were observed for the 6{lambda} separation condition. This result lays the foundation for future work investigating whether a-tDCS may be useful as a visual rehabilitation tool for individuals with central vision loss who are reliant on peripheral vision.

neuroscience↗

bioRxiv2019

Evolutionary Dynamics Do Not Motivate a Single-Mutant Theory of Human Language

AbstractOne of the most controversial hypotheses in cognitive science is the Chomskyan evolutionary conjecture that language arose instantaneously in our species as the result of a single staggeringly fortuitous mutation. Here we analyze the evolutionary dynamics implied by this hypothesis, which has never been formalized. The theory supposes the emergence and fixation of a single mutant (capable of the syntactic operation Merge) during a narrow historical window as a result of frequency-independent selection under a huge fitness advantage in a population of an effective size that is standardly assumed to have been no larger than ~15 000 early humans. We examine this proposal by combining diffusion analysis and extreme value theory to derive a probabilistic formulation of its dynamics. Perhaps counter-intuitively, a macro-mutation is much more unlikely a priori than multiple mutations with smaller fitness effects, yet both hypotheses predict fixation with high conditional probability. The consequences of this asymmetry have not been accounted for previously. Our results diffuse any suggestion that evolutionary reasoning provides an independent rationale for the controversial single-mutant theory of language.\n\nSignificance statementIn recent years, Chomsky and colleagues have sought support for their minimalist theory of the language faculty from evolutionary considerations. They have argued for a spontaneous emergence of a mutation conferring an advantage for thought independent of communication. Here for the first time a formalization of this view is offered, and contrasted with a more gradual evolutionary scenario. The outcome of our analysis argues against the Chomskyan view.

evolutionary biology↗

bioRxiv2017

Evolving building blocks of rhythm: How human cognition creates music via cultural transmission

Musical rhythm, in all its cross-cultural diversity, exhibits several commonalities across world cultures. Traditionally, music research has been split in two fields. Some scientists focused on musicality, namely the human biocognitive predispositions for music, with an emphasis on cross-cultural similarities. Other scholars investigated music, seen as cultural product, focusing on the large variation in world musical cultures. Recent experiments found deep connections between music and musicality, reconciling these opposing views. Here we address the question of how individual cognitive biases affect the process of cultural evolution of music. Data from two experiments is analyzed using two different, complementary techniques. In the experiments, participants hear drumming patterns and imitate them. These patterns are then given to the same or another participant to imitate. The structure of these - initially random - patterns is tracked down to later experimental generations. Frequentist statistics show how participants biases are amplified by cultural transmission, making drumming patterns more structured. Structure is achieved faster than in transmission within, rather than between, participants. A Bayesian model approximates the motif structures participants learned and created. Overall, our data and model show that individual biases for musicality play a central role in shaping cultural transmission of musical rhythm.

animal behavior and cognition↗