Probing basal ganglia functions by saccade eye movements

Abstract

The basal ganglia (BG) are a group of subcortical structures involved in diverse functions, such as motor, cognition and emotion. However, the BG do not control these functions directly, but rather modulate functional processes occurring in structures outside the BG. The BG form multiple functional loops, each of which controls different functions with similar architectures. Accordingly, to understand the modulatory role of the BG, it is strategic to uncover the mechanisms of signal processing within specific functional loops that control simple neural circuits outside the BG, and then extend the knowledge to other BG loops. The saccade control system is one of the best-understood neural circuits in the brain. Furthermore, sophisticated saccade paradigms have been used extensively in clinical research in patients with BG disorders as well as in basic research in behaving monkeys. In this review, we describe recent advances of BG research from the viewpoint of saccade control. Specifically, we account for experimental results from neuroimaging and clinical studies in humans based on the updated knowledge of BG functions derived from neurophysiological experiments in behaving monkeys by taking advantage of homologies in saccade behavior. It has become clear that the traditional BG network model for saccade control is too limited to account for recent evidence emerging from the roles of subcortical nuclei not incorporated in the model. Here, we extend the traditional model and propose a new hypothetical framework to facilitate clinical and basic BG research and dialogue in the future.

Neural networks related to pro-saccades and anti-saccades revealed by independent component analysis

“…The FEF is involved with both reflexive and volitional saccade initiation, whereas the SEF is responsible for volitional saccade generation (Ettinger et al, 2008a;McDowell et al, 2008;Munoz and Everling, 2004;Pierrot-Deseilligny et al, 2004). The putamen has been associated with the volitional eye movement (Petit et al, 1993;Neggers et al, 2012); however, its exact function is still unclear (Watanabe and Munoz, 2011).…”

Cognition and Eye Movements

“…The ocular motor networks substantially overlie the hemispheric attentional systems in frontal, temporal, and parietal lobes (7), interacting at many levels (8)(9)(10)(11)(12)(13)(14)(15)(16)(17). Cognitive processes are most readily examined with saccades.…”

Saccadic eye movements in Parkinson′s disease

“…[345678910] Saccade preparation or planning, triggering, execution and other saccadic functions are under control of distributed neural network involving cortical and subcortical structures. Subcortical structures like basal ganglia (BG), superior colliculus (SC), thalamus, brainstem and cerebellum and cortical structures like parietal and frontal cortices are major areas involved in saccadic eye movement [Fig.…”

“…In BG, caudate nucleus (CN), subthalamic nucleus (STN), substantia nigra pars reticulate (SNr), external segment of globus pallidus (GPe) and internal segment of globus pallidus (GPi) are major components involved in modulating saccadic movement. [591020] The main output structure of the BG circuitry is SNr which has inhibitory influence on SC through GABAergic neurons and it suppresses saccadic initiation. Modulation of firing rates of SNr/GPi neurons facilitates or inhibits saccadic movement.…”