Biology subjects

Acar, K.

Publications and source records attributed to Acar, K..

4 recordsLinked to original sources

bioRxiv2026

The role of the locus coeruleus in eye movements during perceptual decision making

The locus coeruleus (LC) is the primary source of norepinephrine in the brain and has been implicated in the processes of attention, arousal, and perceptual decision making. Although prior work has linked transient LC activation to both sensory stimulus processing and motor processing, the precise contribution of LC to the distinct sensory and motor components of perceptual decisions remains unclear. Here, we recorded the spiking activity of single LC neurons in rhesus macaques while they performed a visual two-alternative forced-choice change detection task with a saccadic report, designed to cleanly dissociate sensory and motor contributions to LC activity. We found that the large majority of recorded neurons showed robust increases in response tightly locked to the choice saccade, while only a small fraction showed significant responses to the visual stimuli. Saccade-aligned LC responses did not vary with behavioral outcome, perceptual difficulty, reaction time, or session-wide fluctuations in perceptual sensitivity and criterion, indicating that LC motor-related signals were dissociated from perceptual performance. Together, these results demonstrated the existence of a subpopulation of LC neurons whose activity was tightly coupled to oculomotor output across both voluntary and involuntary eye movements during perceptual decision making, but were independent of perceptual decision accuracy. Our findings support a role for LC in facilitating motor preparation and execution in response to behaviorally significant sensory events.

neuroscience↗

bioRxiv2020

Stock market fluctuations impact the emotional brain on a population level.

The stock market is a bellwether of socio-economic changes that may directly affect individual well-being. Using large-scale UK-biobank data generated over 14 years, we applied specification curve analysis to rigorously identify significant associations between the local stock market index (FTSE100) and 479,791 UK residents mood, as well as their alcohol intake and blood pressure adjusting the results for a large number of potential confounders, including age, sex, linear and non-linear effects of time, research site, other stock market indexes. Furthermore, we found similar associations between FTSE100 and volumetric measures of affective brain regions in a subsample (n=39,755; measurements performed over 5.5 years), which were particularly strong around phase transitions characterized by maximum volatility in the market. The main findings did not depend on applied effect-size estimation criteria (linear methods or mutual information criterion) and were replicated in two independent US-based studies (Parkinsons Progression Markers Initiative; n=424; performed over 2,5 years and MyConnectome; n=1; 81 measurements over 1,5 years). Our results suggest that phase transitions in the society, indexed by stock market, exhibit close relationships with human mood, health and the affective brain from an individual to population level.

neuroscience↗

bioRxiv2020

Slow drift of neural activity as a signature of impulsivity in macaque visual and prefrontal cortex

An animals decision depends not only on incoming sensory evidence but also on its fluctuating internal state. This internal state is a product of cognitive factors, such as fatigue, motivation, and arousal, but it is unclear how these factors influence the neural processes that encode the sensory stimulus and form a decision. We discovered that, over the timescale of tens of minutes during a perceptual decision-making task, animals slowly shifted their likelihood of reporting stimulus changes. They did this unprompted by task conditions. We recorded neural population activity from visual area V4 as well as prefrontal cortex, and found that the activity of both areas slowly drifted together with the behavioral fluctuations. We reasoned that such slow fluctuations in behavior could either be due to slow changes in how the sensory stimulus is processed or due to a process that acts independently of sensory processing. By analyzing the recorded activity in conjunction with models of perceptual decision-making, we found evidence for the slow drift in neural activity acting as an impulsivity signal, overriding sensory evidence to dictate the final decision. Overall, this work uncovers an internal state embedded in the population activity across multiple brain areas, hidden from typical trial-averaged analyses and revealed only when considering the passage of time within each experimental session. Knowledge of this cognitive factor was critical in elucidating how sensory signals and the internal state together contribute to the decision-making process.

neuroscience↗

bioRxiv2019

Altered functional interactions between neurons in primary visual cortex of macaque monkeys with experimental amblyopia

Amblyopia, a disorder in which vision through one of the eyes is degraded, arises because of defective processing of information by the visual system. Amblyopia often develops in humans after early misalignment of the eyes (strabismus), and can be simulated in macaque monkeys by artificially inducing strabismus. In such amblyopic animals, single-unit responses in primary visual cortex (V1) are appreciably reduced when evoked by the amblyopic eye compared to the other (fellow) eye. However, this degradation in single V1 neuron responsivity is not commensurate with the marked losses in visual sensitivity and resolution measured behaviorally. Here we explored the idea that changes in patterns of coordinated activity across populations of V1 neurons may contribute to degraded visual representations in amblyopia, potentially making it more difficult to read out evoked activity to support perceptual decisions. We studied the visually-evoked activity of V1 neuronal populations in three macaques (M. nemestrina) with strabismic amblyopia and in one control. Activity driven through the amblyopic eye was diminished, and these responses also showed more interneuronal correlation at all stimulus contrasts than responses driven through the fellow eye or responses in the control. A decoding analysis showed that responses driven through the amblyopic eye carried less visual information than other responses. Our results suggest that part of the reduced visual capacity of amblyopes may be due to changes in the patterns of functional interaction among neurons in V1.\n\nNew and noteworthyAmblyopia is a developmental disorder of visual processing that reduces visual function and changes the visual responses of cortical neurons in macaque monkeys. The neuronal and behavioral changes are not always well correlated. We found that the interactions among neurons in the visual cortex of monkeys with amblyopia are also altered. These changes may contribute to amblyopic visual deficits by diminishing the amount of information relayed by neuronal populations driven by the amblyopic eye.

neuroscience↗