Biology subjects

Zokaei, N.

Publications and source records attributed to Zokaei, N..

4 recordsLinked to original sources

bioRxiv2024

Comparing the impact of contextual associations and statistical regularities in visual search and attention orienting

During visual search, we quickly learn to attend to an objects likely location. Research has shown that this process can be guided by learning target locations based on consistent spatial contextual associations or statistical regularities. Here, we tested how these different types of learning aid the utilisation of established memories for different purposes. Participants learned contextual associations or statistical regularities that predicted target locations within different scenes. The consequences of this learning for subsequent performance were then evaluated on attention-orienting and memory-recall tasks. Participants demonstrated facilitated attention-orienting and recall performance based on both contextual associations and statistical regularities. Contextual associations facilitated attention orienting with a different time course compared to statistical regularities. Benefits to memory-recall performance depended on the alignment between the learned association or regularity and the recall demands. The distinct patterns of behavioural facilitation by contextual associations and statistical regularities show how different forms of long-term memory may influence neural information processing through different modulatory mechanisms.

neuroscience↗

bioRxiv2021

Reduced cortico-muscular beta coupling in Parkinsons disease predicts motor impairment

Long-range communication through the motor system is thought to be facilitated by phase coupling between neural activity in the 15-30 Hz beta range. During periods of sustained muscle contraction (grip), such coupling is manifest between motor cortex and the contralateral forearm muscles - measured as the cortico-muscular coherence (CMC). We examined alterations in CMC in individuals with Parkinsons disease (PD), while equating grip strength between individuals with PD (off their medication) and healthy control participants. We show a marked reduction in beta CMC in the PD group, even though the grip strength was comparable between the two groups. Moreover, the reduced CMC was related to motor symptoms, so that individuals with lower CMC also displayed worse motor symptoms. These findings highlight the CMC as a simple, effective, and clinically relevant neural marker of PD pathology, with the potential to aid monitoring of disease progression and the efficacy of novel treatments for PD.

neuroscience↗

bioRxiv2021

Transient beta activity and connectivity during sustained motor behaviour

Neural oscillations are thought to play a central role in orchestrating activity states between distant neural populations. In humans, long-range neural connectivity has been particularly well characterised for 13-30 Hz beta activity which becomes phase coupled between the motor cortex and the contralateral muscle during isometric contraction. Based on this and related observations, beta activity and connectivity have been linked to sustaining stable cognitive and motor states - or the status quo - in the brain. Recently, however, beta activity has been shown to be short-lived, as opposed to sustained - though so far this has been reported for regional beta activity in tasks without sustained motor demands. Here, we measured magnetoencephalography (MEG) and electromyography (EMG) in 18 human participants performing an isometric-contraction (gripping) task designed to yield sustained behavioural output. If cortico-muscular beta connectivity is directly responsible for sustaining a stable motor state, then beta activity should be (or become) sustained in this context. In contrast, we found that beta activity and connectivity with the downstream muscle were transient, even when participants engaged in sustained gripping. Moreover, we found that sustained motor requirements did not prolong beta-event duration in comparison to rest. These findings suggest that long-range neural synchronisation may entail short bursts of frequency-specific connectivity, even when task demands - and behaviour - are sustained. HighlightsO_LITrial-average 13-30 Hz beta activity and connectivity with the muscle appear sustained during stable motor behaviour C_LIO_LISingle-trial beta activity and connectivity are short-lived, even when motor behaviour is sustained C_LIO_LISustained task demands do not prolong beta-event duration in comparison to resting state C_LI

neuroscience↗

bioRxiv2017

A neural model of working memory

Working memory, the ability to keep recently encountered information available for immediate processing, has been proposed to rely on two mechanisms that appear difficult to reconcile: selfsustained neural firing, or the opposite--activity-silent synaptic traces. Here we show that both phenomena can co-exist within a unified system in which neurons hold information in both activity and synapses. Rapid plasticity in flexibly-coding neurons allows features to be bound together into objects, with an important emergent property being the focus of attention. One memory item is held by persistent activity in an attended or \"focused\" state, and is thus remembered better than other items. Other, previously attended items can remain in memory but in the background, encoded in activity-silent synaptic traces. This dual functional architecture provides a unified common mechanism accounting for a diverse range of perplexing attention and memory effects that have been hitherto difficult to explain in a single theoretical framework.

neuroscience↗