Eyes as a marker of CNS activity - relevance to dopaminergic functioning My experiences not being able to open my eyes [1] made me interested in it's use as a marker of CNS activity. In most of the cases apraxia of eyelid opening has been reported in association with basal ganglia diseases Eye blink rate (EBR) is a behavioral index highly correlated with frontostriatal dopaminergic activity. Disorders related to abnormal DA function show atypical EBRs: It is noted in Parkinson's spontaneous eye blink rate is decreased, so too ADHD and ASD, whereas in schizophrenia it is generally enhanced. It can be used as a non-invasive measure of dopaminergic related sustained attention and fatigue [2]. EBR predicts DA-related cognitive performance [3] and EBR might predict improvement in performance especially on tasks that require a flexible mind [4]. Striatal D1 and D2 binding has been associated with eye blink rate [5] and other disorders affecting dopamine pathways including behavioural and substance addictions (drug addiction, pathological gambling) have revealed differences in eye blink rate, where it is consistent with their reduced D2 receptor density. EBR is suggested to be a "general phenomenon which occurs whenever the interaction with the environment requires an active and controlled allocation of attentional resources, and would reflect the balance of the central dopaminergic tone which is disrupted under strong attentional demands" EBR reliably predicts the efficiency in inhibiting unwanted action tendencies, inhibitory control [6] and EBR reliably predicts behavioral performance on cognitive tasks that have been associated with dopaminergic functioning. Dopamine depletion, characterised by decreased happiness, euphoria, energy, talkativeness, vigor, and attentiveness, and in increased sleepiness, fatigue, sedation, and alterations to eye blink rate (EBR) [7] has been linked to decreased performance in neuropsychological testing of attention and executive functions, in which these patients consistently perform with an increased cognitive inflexibility and an inability to shift their attention to relevant information in order to comply with environmental demands There is a bi-directional modulation of effort-related choice, such that reduced DA transmission biases animals towards low effort alternatives, and enhanced DA transmission increases selection of high effort alternatives [1] https://www.ncbi.nlm.nih.gov/books/NBK560542/ [2] https://www.researchgate.net/.../Spontaneous-eye-blink ... [3] https://doi.org/10.1016/j.neubiorev.2016.08.020 [4] https://doi.org/10.3389/fpsyg.2014.01101 [5] https://www.nature.com/articles/s42003-022-03979-5 1 [6] https://link.springer.com/article/10.1007/s00221-009-1862-x [7] https://doi.org/10.1016/S0091-3057(02)01028-6 2