Distinct context- and content-dependent population codes in superior colliculus during sensation and action.

Sensorimotor transformation is the process of first sensing an object in the environment and then producing a movement in response to that stimulus. For visually guided saccades, neurons in the superior colliculus (SC) emit a burst of spikes to register the appearance of stimulus, and many of the same neurons discharge another burst to initiate the eye movement. We investigated whether the neural signatures of sensation and action in SC depend on context.

Rapid Input-Output Transformation between Local Field Potential and Spiking Activity during Sensation but not Action in the Superior Colliculus.

Sensorimotor transformation is the sequential process of registering a sensory signal in the environment and then responding with the relevant movement at an appropriate time. For visually guided eye movements, neural signatures in the form of spiking activity of neurons have been extensively studied along the dorsoventral axis of the superior colliculus (SC). In contrast, the local field potential (LFP), which represents the putative input to a region, remains largely unexplored in the SC.

Drifting population dynamics with transient resets characterize sensorimotor transformation in the monkey superior colliculus.

To produce goal-directed eye movements known as saccades, we must channel sensory input from our environment through a process known as sensorimotor transformation. The behavioral output of this phenomenon (an accurate eye movement) is straightforward, but the coordinated activity of neurons underlying its dynamics is not well understood. We searched for a neural correlate of sensorimotor transformation in the activity patterns of simultaneously recorded neurons in the superior colliculus (SC) of three male rhesus monkeys performing a visually guided, delayed saccade task.

Ventral premotor cortex encodes task relevant features during eye and head movements.

Visual exploration of the environment is achieved through gaze shifts or coordinated movements of the eyes and the head. The kinematics and contributions of each component can be decoupled to fit the context of the required behavior, such as redirecting the visual axis without moving the head or rotating the head without changing the line of sight. A neural controller of these effectors, therefore, must show code relating to multiple muscle groups, and it must also differentiate its code based on context.

Decoding the Time Course of Spatial Information from Spiking and Local Field Potential Activities in the Superior Colliculus.

Place code representation is ubiquitous in circuits that encode spatial parameters. For visually guided eye movements, neurons in many brain regions emit spikes when a stimulus is presented in their receptive fields and/or when a movement is directed into their movement fields. Crucially, individual neurons respond for a broad range of directions or eccentricities away from the optimal vector, making it difficult to decode the stimulus location or the saccade vector from each cell's activity.

Population temporal structure supplements the rate code during sensorimotor transformations.

Sensorimotor transformations are mediated by premotor brain networks where individual neurons represent sensory, cognitive, and movement-related information. Such multiplexing poses a conundrum-how does a decoder know precisely when to initiate a movement if its inputs are active at times when a movement is not desired (e.g.

Sensorimotor transformation elicits systematic patterns of activity along the dorsoventral extent of the superior colliculus in the macaque monkey.

The superior colliculus (SC) is an excellent substrate to study sensorimotor transformations. To date, the spatial and temporal properties of population activity along its dorsoventral axis have been inferred from single electrode studies. Here, we recorded SC population activity in non-human primates using a linear multi-contact array during delayed saccade tasks.

Instantaneous Midbrain Control of Saccade Velocity.

The ability to interact with our environment requires the brain to transform spatially represented sensory signals into temporally encoded motor commands for appropriate control of the relevant effectors. For visually guided eye movements, or saccades, the superior colliculus (SC) is assumed to be the final stage of spatial representation, and instantaneous control of the movement is achieved through a rate code representation in the lower brain stem. We investigated whether SC activity in nonhuman primates (Macaca mulatta, 2 male and 1 female) also uses a dynamic rate code, in addition to the spatial representation.

The superior colliculus and the steering of saccades toward a moving visual target.

Following the suggestion that a command encoding current target location feeds the oculomotor system during interceptive saccades, we tested the involvement of the deep superior colliculus (dSC). Extracellular activity of 52 saccade-related neurons was recorded in three monkeys while they generated saccades to targets that were static or moving along the preferred axis, away from (outward) or toward (inward) a fixated target with a constant speed (20°/s). Vertical and horizontal motions were tested when possible.

Removal of inhibition uncovers latent movement potential during preparation.

The motor system prepares for movements well in advance of their execution. In the gaze control system, the dynamics of preparatory neural activity have been well described by stochastic accumulation-to-threshold models. However, it is unclear whether this activity has features indicative of a hidden movement command.

Disruption of Fixation Reveals Latent Sensorimotor Processes in the Superior Colliculus.

Unlabelled: Executive control of voluntary movements is a hallmark of the mammalian brain. In the gaze-control network, this function is thought to be mediated by a critical balance between neurons responsible for generating movements and those responsible for fixating or suppressing movements, but the nature of this balance between the relevant elements-saccade-generating and fixation-related neurons-remains unclear. Specifically, it has been debated whether the two functions are necessarily coupled (i.

Context cue-dependent saccadic adaptation in rhesus macaques cannot be elicited using color.

When the head does not move, rapid movements of the eyes called saccades are used to redirect the line of sight. Saccades are defined by a series of metrical and kinematic (evolution of a movement as a function of time) relationships. For example, the amplitude of a saccade made from one visual target to another is roughly 90% of the distance between the initial fixation point (T0) and the peripheral target (T1).

Study of extrusion behaviour and porridge making characteristics of wheat and guava blends.

Extrusion cooking studies were carried out with a view to develop an instant porridge from wheat grits and guava pulp at different levels from 10 to 50 %. The mixtures were dried to bring down the moisture content to 12, 15 or 18 % and processed using twin screw extruder. The properties of extrudates (expansion ratio and density) and porridge (water absorption index, water solubility index and sensory quality) were studied.

Time course of motor preparation during visual search with flexible stimulus-response association.

Whether allocation of visuospatial attention can be divorced from saccade preparation has been the subject of intense research efforts. A variant of the visual search paradigm, in which a feature singleton indicates that the correct saccade should be directed to it (prosaccade) or to the opposite distractor (antisaccade), has been influential in addressing this core topic. We performed a causal assessment of this controversy by delivering an air puff to one eye to invoke the trigeminal blink reflex as monkeys performed this visual search task.

Blink perturbation effects on saccades evoked by microstimulation of the superior colliculus.

Current knowledge of saccade-blink interactions suggests that blinks have paradoxical effects on saccade generation. Blinks suppress saccade generation by attenuating the oculomotor drive command in structures like the superior colliculus (SC), but they also disinhibit the saccadic system by removing the potent inhibition of pontine omnipause neurons (OPNs). To better characterize these effects, we evoked the trigeminal blink reflex by delivering an air puff to one eye as saccades were evoked by sub-optimal stimulation of the SC.

The relative impact of microstimulation parameters on movement generation.

Microstimulation is widely used in neurophysiology to characterize brain areas with behavior and in clinical therapeutics to treat neurological disorder. Current intensity and frequency, which respectively influence activation patterns in spatial and temporal domains, are typically selected to elicit a desired response, but their effective influence on behavior has not been thoroughly examined. We delivered microstimulation to the primate superior colliculus while systematically varying each parameter to capture effects of a large range of parameter space.

A test of spatial temporal decoding mechanisms in the superior colliculus.

Population coding is a ubiquitous principle in the nervous system for the proper control of motor behavior. A significant amount of research is dedicated to studying population activity in the superior colliculus (SC) to investigate the motor control of saccadic eye movements. Vector summation with saturation (VSS) has been proposed as a mechanism for how population activity in the SC can be decoded to generate saccades.

Interactions between gaze-evoked blinks and gaze shifts in monkeys.

Rapid eyelid closure, or a blink, often accompanies head-restrained and head-unrestrained gaze shifts. This study examines the interactions between such gaze-evoked blinks and gaze shifts in monkeys. Blink probability increases with gaze amplitude and at a faster rate for head-unrestrained movements.

Order of operations for decoding superior colliculus activity for saccade generation.

To help understand the order of events that occurs when generating saccades, we simulated and tested two commonly stated decoding models that are believed to occur in the oculomotor system: vector averaging (VA) and center-of-mass. To generate accurate saccades, each model incorporates two required criteria: 1) a decoding mechanism that deciphers a population response of the superior colliculus (SC) and 2) an exponential transformation that converts the saccade vector into visual coordinates. The order of these two criteria is used differently within each model, yet the significance of the sequence has not been quantified.

Motor functions of the superior colliculus.

The mammalian superior colliculus (SC) and its nonmammalian homolog, the optic tectum, constitute a major node in processing sensory information, incorporating cognitive factors, and issuing motor commands. The resulting action-to orient toward or away from a stimulus-can be accomplished as an integrated movement across oculomotor, cephalomotor, and skeletomotor effectors. The SC also participates in preserving fixation during intersaccadic intervals.

Matching the oculomotor drive during head-restrained and head-unrestrained gaze shifts in monkey.

High-frequency burst neurons in the pons provide the eye velocity command (equivalently, the primary oculomotor drive) to the abducens nucleus for generation of the horizontal component of both head-restrained (HR) and head-unrestrained (HU) gaze shifts. We sought to characterize how gaze and its eye-in-head component differ when an "identical" oculomotor drive is used to produce HR and HU movements. To address this objective, the activities of pontine burst neurons were recorded during horizontal HR and HU gaze shifts.

A novel, easy, non-operative method of treating prolapsed colostomy.

Colostomy prolapse is a major cause of morbidity in paediatric patients with Hirschsprung's disease and anorectal malformations. Although it is commonly associated with the distal loop of a transverse colostomy, a sigmoid stoma can also be affected. We report six babies with anorectal malformations between day 10 and 6 months presenting with incessant crying and irritability following prolapsed colostomy stomas.

Dynamics of primate oculomotor plant revealed by effects of abducens microstimulation.

Despite their importance for deciphering oculomotor commands, the mechanics of the extraocular muscles and orbital tissues (oculomotor plant) are poorly understood. In particular, the significance of plant nonlinearities is uncertain. Here primate plant dynamics were investigated by measuring the eye movements produced by stimulating the abducens nucleus with brief pulse trains of varying frequency.

Coordination of eye and head components of movements evoked by stimulation of the paramedian pontine reticular formation.

Constant frequency microstimulation of the paramedian pontine reticular formation (PPRF) in head-restrained monkeys evokes a constant velocity eye movement. Since the PPRF receives significant projections from structures that control coordinated eye-head movements, we asked whether stimulation of the pontine reticular formation in the head-unrestrained animal generates a combined eye-head movement or only an eye movement. Microstimulation of most sites yielded a constant-velocity gaze shift executed as a coordinated eye-head movement, although eye-only movements were evoked from some sites.

Effect of reversible inactivation of superior colliculus on head movements.

Because of limitations in the oculomotor range, many gaze shifts must be accomplished using coordinated movements of the eyes and head. Stimulation and recording data have implicated the primate superior colliculus (SC) in the control of these gaze shifts. The precise role of this structure in head movement control, however, is not known.