Cerebral Changes during Performance of Overlearned Arbitrary Visuomotor Associations

A prevailing question in sensorimotor research is the integration of sensory signals with abstract behavioral rules (contexts) and how this results in decisions about motor actions. We used neural network models to study how context-specific visuomotor remapping may depend on the functional connectivity among multiple layers. Networks were trained to perform different rotational visuomotor associations, depending on the stimulus color (a nonspatial context signal). In network I, the context signal was propagated forward through the network (bottom-up), whereas in network II, it was propagated backwards (top-down). During the presentation of the visual cue stimulus, both networks integrate the context with the sensory information via a mechanism similar to the classic gain field. The recurrence in the networks hidden layers allowed a simulation of the multimodal integration over time. Network I learned to perform the proper visuomotor transformations based on a context-modulated memory of the visual cue in its hidden layer activity. In network II, a brief visual response, which was driven by the sensory input, is quickly replaced by a context-modulated motor-goal representation in the hidden layer. This happens because of a dominant feedback signal from the output layer that first conveys context information, and then, after the disappearance of the visual cue, conveys motor goal information. We also show that the origin of the context information is not necessarily closely tied to the top-down feedback. However, we suggest that the predominance of motor-goal representations found in the parietal cortex during context-specific movement planning might be the consequence of strong top-down feedback originating from within the parietal lobe or from the frontal lobe.

Section: Anatomical-physiological Interpretations Of the Network Connmentioning

confidence: 78%

Gain Mechanisms for Contextually Guided Visuomotor Transformations

Brozović

Gail²,

Andersen³

2007

“…We found that LIP neurons also responded robustly in this task, simultaneously encoding the location of the cue and the active limb. This suggests that parietal association areas are instrumental for linking relevant visuospatial and motor variables, not only for goal-directed but also for symbolically cued behaviors (Toth and Assad, 2002;Grol et al, 2006). Selectivity for cue location was the primary and most prevalent signal in the LIP, because strong cue-evoked activity was found in the vast majority of neurons and correlated with behavioral reaction time mainly independently of the active limb.…”

Section: Discussionmentioning

confidence: 99%

Integration of Visuospatial and Effector Information during Symbolically Cued Limb Movements in Monkey Lateral Intraparietal Area

Oristaglio

Schneider²,

Balan³

et al. 2006

131

Natural behavior requires close but flexible coordination between attention, defined as selection for perception, and action. In recent years a distributed network including the lateral intraparietal area (LIP) has been implicated in visuospatial selection for attention and rapid eye movements (saccades), but the relation between the attentional and motor functions of this area remains unclear. Here we tested LIP neurons in a task that involved not an ocular but a manual operant response. Monkeys viewed a display containing one cue and several distractors and reported the orientation of the cue (right-or left-facing) by releasing one of two bars grasped, respectively, with the right or left hand. The movement in this task thus was associated with (cued by), but not directed toward, the visual stimulus. A large majority of neurons responded more when the cue rather than when a distractor was in their receptive field, suggesting that they contribute to the attentional selection of the cue. A fraction of these neurons also was modulated by limb release, thus simultaneously encoding cue location and the active limb. The results suggest that the LIP links behaviorally relevant visual information with motor variables relevant for solving a task in a wide range of circumstances involving goal-directed or symbolically cued movements and eye as well as limb movements. A central function of the LIP may be to coordinate visual and motor selection during a wide variety of behaviors.

“…Dual-task paradigms have been consistently used as rigorous tests of automaticity (Passingham, 1996;Oliveira et al, 1998;Poldrack et al, 2005;Grol et al, 2006). We assessed the level of automaticity attained in both conditions to determine the robustness of performance to distractors.…”

Section: Taskmentioning

confidence: 99%

Cerebellar Plasticity and the Automation of First-Order Rules

Balsters¹,

Ramnani²

2011

Theories of corticocerebellar function propose roles for the cerebellum in automating motor control, a process thought to depend on plasticity in cerebellar circuits that exchange information with the motor cortex. Little is known, however, about automating behaviors beyond the motor domain. The present study tested the hypothesis that cerebellar plasticity also subserves the development of automaticity in behavior based on low-order rules. Human subjects were required to learn two sets of first-order rules in which visual stimuli of different shapes each arbitrarily instructed a particular finger movement. We used event-related functional magnetic resonance imaging to scan subjects while these response rules became increasingly automatic with practice, as assessed with a dual-task procedure. We found that the amplitude of the blood oxygenation level-dependent signal gradually decreased as a function of practice, as responses became increasingly automatic, and that this effect was greater for a set of rules that became automatic rapidly compared with a second set, which became automatic more slowly. These trial-by-trial activity changes occurred in Crus I of cerebellar cortical lobule HVIIA, in which neurons exchange information with the prefrontal cortex rather than the motor cortex. Activity in Crus I was time locked specifically to the processing of these rules, rather than to subsequent actions. The results support the hypothesis that decreases in cerebellar cortical activity underlie the automation of behavior, whether related to motor control and motor cortex or to response rules and prefrontal cortex.