Purkinje Cell Activity During Suppression of Voluntary Eye Movements in Rhesus Macaques

Conscious control of actions helps us to reach our goals by suppressing responses to distracting external stimuli. The cerebellum has been suggested to complement cerebral control of inhibition of targeted movements (conscious control), though by what means, remains unclear. By measuring Purkinje cell (PC) responses during antisaccades, we show that the cerebellum not only plays a role in the execution of eye movements, but also in during the volitional inhibition thereof. We found that simple spike (SS) modulation during instruction and execution of prosaccades and antisaccades was prominent in PCs of both medial and lateral cerebellum, showing distinct, time-ordered sequences, but each with different sensitivities for execution and trial-history. SS activity in both regions modulated bidirectionally, with both facilitation (increasing SS firing) and suppression (decreasing SS firing) PCs showing firing-rate changes associated with instruction and execution, respectively. These findings show that different cerebellar regions can contribute to behavioral control and inhibition, but with different propensities, enriching the cerebellar machinery in executive control.

Influence of voluntary eye movements on the stepping test

Antecedentes: Sabe-se que o comportamento locomotor de um indivíduo durante o teste de piso de Fukuda – Unterberger é modificado pela rotação voluntária do pescoço ou rotação reflexa do olho após a interposição de um prisma de baixa potência. Objetivo: Mas quais são os efeitos da versão voluntária do olho? Método: Três parâmetros do teste de degrau foram observados em uma coorte de 23 sujeitos rigorosamente selecionados, durante a execução do teste em cinco posições da versão ocular voluntária. Resultados: Observou-se um movimento de rotação ipsilateral à versão ocular, já aparente para uma versão de 2,5 ° que foi estatisticamente significante (teste t de Student). Conclusão: Voluntários ou reflexos, movimentos oculares versão têm o mesmo efeito na atividade tônica postural.

Eye Movements Interfere With Limb Motor Control in Stroke Survivors

Background. Humans use voluntary eye movements to actively gather visual information during many activities of daily living, such as driving, walking, and preparing meals. Most stroke survivors have difficulties performing these functional motor tasks, and we recently demonstrated that stroke survivors who require many saccades (rapid eye movements) to plan reaching movements exhibit poor motor performance. However, the nature of this relationship remains unclear. Objective. Here we investigate if saccades interfere with speed and smoothness of reaching movements in stroke survivors, and if excessive saccades are associated with difficulties performing functional tasks. Methods. We used a robotic device and eye tracking to examine reaching and saccades in stroke survivors and age-matched controls who performed the Trail Making Test, a visuomotor task that uses organized patterns of saccades to plan reaching movements. We also used the Stroke Impact Scale to examine difficulties performing functional tasks. Results. Compared with controls, stroke survivors made many saccades during ongoing reaching movements, and most of these saccades closely preceded transient decreases in reaching speed. We also found that the number of saccades that stroke survivors made during ongoing reaching movements was strongly associated with slower reaching speed, decreased reaching smoothness, and greater difficulty performing functional tasks. Conclusions. Our findings indicate that poststroke interference between eye and limb movements may contribute to difficulties performing functional tasks. This suggests that interventions aimed at treating impaired organization of eye movements may improve functional recovery after stroke.

Bárány’s Life in Uppsala and His Work with Lorente de Nó

Lorente de Nó came to Uppsala, Sweden, in 1924 to work with Robert Bárány, with the goal of studying the central nervous system pathways of the vestibular nystagmus response. Bárány’s 1907 book described a patient with a lesion involving the reticular formation of the pons close to the abducens nucleus who could generate only the slow phase of nystagmus. With stimulation, the patient’s eyes slowly deviated to one side and became pinned. The patient also had a loss of voluntary eye movements. Bárány concluded that there must be separate centers in the brainstem for the production of the slow and fast phases of nystagmus. He speculated that the center for generating fast phases was in the reticular substance next to the abducens nucleus and that this component was under the influence of cortical control. Nó would go on to perform studies of these central pathways for generating nystagmus in rabbit.