Time-course of population activity along the dorsoventral extent of the superior colliculus during delayed saccade tasks

Abstract

20The superior colliculus (SC) is an excellent substrate to study functional organization of 21 sensorimotor transformations. We used linear multi-contact array recordings to analyze the spatial and 22 temporal properties of population activity along the SC dorsoventral axis during delayed saccade tasks. 23During the visual epoch, information appeared first in dorsal layers and systematically later in ventral layers. 24In the ensuing delay period, the laminar organization of low-spiking rate activity matched that of the visual 25 epoch. During the pre-saccadic epoch, spiking activity emerged first in a more ventral layer, ~100ms before 26 saccade onset. This buildup of activity appeared later on nearby neurons situated both dorsally and 27 ventrally, culminating in a synchronous burst across the dorsoventral axis, ~28ms before saccade onset. 28 Stimulation of individual contacts on the laminar probe produced saccades of similar vectors. Collectively, 29 the results reveal a principled spatiotemporal organization of SC population activity underlying sensorimotor 30 transformation for the control of gaze. 31 32 Introduction 33Our interactions with the environment are mediated via brain networks that transform sensory 34 signals to motor actions at the appropriate time. In the context of gaze control, this sensorimotor 35 transformation entails processing of incoming visual information and generating a movement command to 36 appropriately redirect the line of sight. The superior colliculus (SC) in the midbrain modulates its activity in 37 response to both stimulus presentation and movement generation, as well as during the interval between 38 the two events. Like cortex, the SC is composed of distinct layers. Its superficial layers are predominantly 39 driven by visual processing structures like the retina and primary visual cortex, while its deeper layers 40 communicate a broad spectrum of information with many cortical and noncortical areas [1][2][3] . It also has a 41 canonical organization with established microcircuits for communication both within and across layers 4 . 42Finally, it has a topographic representation of visual space and for generation of gaze shifts to those 43 locations 5 . Thus, the SC is ideally suited to study the neural correlates of sensorimotor transformation. 44Despite a wealth of knowledge about the anatomical organization of the SC and the functional 45 properties of individual SC neurons, current understanding about the link between structural and functional 46 organization at the population level is limited. For instance, it is unclear whether the properties of individual 47 neurons exhibit systematic spatiotemporal organization during the sensorimotor transformation, and how 48 such organization is linked to the microarchitecture of the SC network. Bridging structure with function helps 49 to not only understand the computations underlying the transformation but also to build biologically-inspired 50 network models of sensorimotor learning and behavior 6,7 . 51Linear microelectrodes...

Spatiotemporal transformations for gaze control

“…The methodologies, results, and model described in this review can lead to many more questions, such as: (a) How is the T‐to‐G transformation accomplished through the interaction of neurons within and between different layers of SC and FEF microcircuits? (Basso & May, 2017; Bastos et al., 2012; Chandrasekaran, Peixoto, Newsome, & Shenoy, 2017; Heinzleet al, 2007; Massot, Jagadisan, & Gandhi, 2019; Sajad, Godlove, & Schall, 2019; Shin & Sommer, 2012); (b) How do the spatial codes at the individual neuron and population levels change in other visuomotor behaviors, such as express saccades (latency < 100 ms), in which the temporal visual and motor responses entirely overlap (Dorris, Pare, & Munoz, 1997; Isa, 2002)? ; (c) how does this methodology extend to other areas of the brain involved in gaze control (Bremmer et al., 2016; Schneider, Dominguez‐Vargas, Gibson, Kagan, & Wilke, 2020)?…”