He Cui

Intention, action planning, and decision making in parietal-frontal circuits.

The posterior parietal cortex and frontal cortical areas to which it connects are responsible for sensorimotor transformations. This review covers new research on four components of this transformation process: planning, decision making, forward state estimation, and relative-coordinate representations. These sensorimotor functions can be harnessed for neural prosthetic operations by decoding intended goals (planning) and trajectories (forward state estimation) of movements as well as higher cortical functions related to decision making and potentially the coordination of multiple body parts (relative-coordinate representations).

Posterior Parietal Cortex Encodes Autonomously Selected Motor Plans

The posterior parietal cortex (PPC) of rhesus monkeys has been found to encode the behavioral meaning of categories of sensory stimuli. When animals are instructed with sensory cues to make either eye or hand movements to a target, PPC cells also show specificity depending on which effector (eye or hand) is instructed for the movement. To determine whether this selectivity retrospectively reflects the behavioral meaning of the cue or prospectively encodes the movement plan, we trained monkeys to autonomously choose to acquire a target in the absence of direct instructions specifying which effector to use. Activity in PPC showed strong specificity for effector choice, with cells in the lateral intraparietal area selective for saccades and cells in the parietal reach region selective for reaches. Such differential activity associated with effector choice under identical stimulus conditions provides definitive evidence that the PPC is prospectively involved in action selection and movement preparation.

Movement intention is better predicted than attention in the posterior parietal cortex

We decoded on a trial-by-trial basis the location of visual targets, as a marker of the locus of attention, and intentions to reach and to saccade in different directions using the activity of neurons in the posterior parietal cortex of two monkeys. Predictions of target locations were significantly worse than predictions of movement plans for the same target locations. Moreover, neural signals in the parietal reach region (PRR) gave better predictions of reaches than saccades, whereas signals in the lateral intraparietal area (LIP) gave better predictions of saccades than reaches. Taking together the activity of both areas, the prediction of either movement in all directions became nearly perfect. These results cannot be explained in terms of an attention effect and support the idea of two segregated populations in the posterior parietal cortex, PRR and LIP, that are involved in different movement plans.

Different Representations of Potential and Selected Motor Plans by Distinct Parietal Areas

Traditional theories have considered decision making as a separate neural process occurring before action planning. However, recent neurophysiological studies of spatial target selection have suggested that decision making and motor planning may be performed in an integrated manner. It was proposed that multiple potential plans are concurrently formed and the ultimately selected action simultaneously emerges within the same circuits (Shadlen and Newsome, 2001; Cisek and Kalaska, 2010). In the present study, we recorded from the parietal reach region (PRR) and dorsal area 5 (area 5d) in the posterior parietal cortex (PPC) while monkeys performed a nonspatial effector (saccade vs reach) choice task. The results show that PRR encodes potential and selected reach plans whereas area 5d encodes only selected reach plans, suggesting a serial visuomotor cortical circuitry for nonspatial effector decisions. Thus, there appears to be a different flow of processing for decisions and planning for spatial target selection, which is more integrated, and nonspatial effector decisions between eye and limb movements, which are more serial.

The Posterior Parietal Cortex Encodes in Parallel Both Goals for Double-Reach Sequences

The parietal reach region (PRR) is known to be involved in the preparation of visually guided arm movements to single targets. We explored whether PRR encodes only the target of the next movement or, alternatively, also a subsequent goal in a double-reach sequence. Two monkeys were trained to memorize the locations of two peripheral cues and to prepare for a memory-guided delayed double-reach sequence. On a GO-signal they had to reach in a predefined order to both remembered target locations without breaking eye fixation. The movement goals were arranged such that either the first or the second target was inside the response field of an isolated neuron. We analyzed the neural activity of single cells in PRR during the late memory period between cue offset and the GO-signal. During this memory period, most PRR cells encoded the first as well as the second goal of the planned reaching sequence. The results indicate that the posterior parietal cortex is involved in the spatial planning of more complex action patterns and represents immediate and subsequent movement goals.

Influencing and Interpreting Visual Input: The Role of a Visual Feedback System

Vertebrates are able to visually identify moving objects and orient toward attractive ones or escape if the objects seem threatening. When there is more than one object in the visual field, they can attend to a particular object. The optic tectum (superior colliculus in mammals) (OT/SC) has long

Neural correlates of learning and trajectory planning in the posterior parietal cortex

The posterior parietal cortex (PPC) is thought to play an important role in the planning of visually-guided reaching movements. However, the relative roles of the various subdivisions of the PPC in this function are still poorly understood. For example, studies of dorsal area 5 point to a representation of reaches in both extrinsic (endpoint) and intrinsic (joint or muscle) coordinates, as evidenced by partial changes in preferred directions and positional discharge with changes in arm posture. In contrast, recent findings suggest that the adjacent medial intraparietal area (MIP) is involved in more abstract representations, e.g., encoding reach target in visual coordinates. Such a representation is suitable for planning reach trajectories involving shortest distance paths to targets straight ahead. However, it is currently unclear how MIP contributes to the planning of other types of trajectories, including those with various degrees of curvature. Such curved trajectories recruit different joint excursions and might help us address whether their representation in the PPC is purely in extrinsic coordinates or in intrinsic ones as well. Here we investigated the role of the PPC in these processes during an obstacle avoidance task for which the animals had not been explicitly trained. We found that PPC planning activity was predictive of both the spatial and temporal aspects of upcoming trajectories. The same PPC neurons predicted the upcoming trajectory in both endpoint and joint coordinates. The predictive power of these neurons remained stable and accurate despite concomitant motor learning across task conditions. These findings suggest the role of the PPC can be extended from specifying abstract movement goals to expressing these plans as corresponding trajectories in both endpoint and joint coordinates. Thus, the PPC appears to contribute to reach planning and approach-avoidance arm motions at multiple levels of representation.

Dorsal Parietal Area 5 Encodes Immediate Reach in Sequential Arm Movements

To generate a coherent action sequence, it is essential to integrate all component movements beforehand, and such sequence-related information has been observed in numerous brain regions. However, this high-level sequential plan encompassing multiple motor elements in parallel ultimately must be decomposed into serial motor commands to be executed by the musculoskeletal system. In the present study, we recorded single-neuron activity from dorsal parietal area 5 (area 5d) while monkeys performed a double-reach task, and found that area 5d conveys the immediate upcoming reach, but not the subsequent movement, as opposed to the entire movement sequence being encoded as in other cortical sensorimotor areas. The elementary movement coded in area 5d suggests that unfolding of the motor sequence begins in the parietal-frontal cortex, instead of being exclusively implemented by downstream subcortical and spinal circuits.To generate a coherent action sequence, it is essential to integrate all component movements beforehand, and such sequence-related information has been observed in numerous brain regions. However, this high-level sequential plan encompassing multiple motor elements in parallel ultimately must be decomposed into serial motor commands to be executed by the musculoskeletal system. In the present study, we recorded single-neuron activity from dorsal parietal area 5 (area 5d) while monkeys performed a double-reach task, and found that area 5d conveys the immediate upcoming reach, but not the subsequent movement, as opposed to the entire movement sequence being encoded as in other cortical sensorimotor areas. The elementary movement coded in area 5d suggests that unfolding of the motor sequence begins in the parietal-frontal cortex, instead of being exclusively implemented by downstream subcortical and spinal circuits.

From Intention to Action: Hierarchical Sensorimotor Transformation in the Posterior Parietal Cortex

While there is a large body of evidence in favor of a clustering of representations of body effectors in the posterior parietal cortex, recent advances have revealed a hierarchical organization beyond a flat intentional map composed of functionally distinct subdivisions operating in parallel at same level. In particular, the parietal reach region (PRR) and dorsal area 5 (area 5d) have been found to play distinct roles in visually-guided reach. Abstract Cover Figure Although both the PRR and area 5d have been found to be intimately involved in visually guided reach, several recent studies of reference frame, decision making, and sequential movement suggest that they might play distinct roles in planning and control of reach at different levels of complexity, indicating a hierarchical circuitry participating in translation from abstract intention into concrete action plan.

Predictive encoding of moving target trajectory by neurons in the parabigeminal nucleus

Intercepting momentarily invisible moving objects requires internally generated estimations of target trajectory. We demonstrate here that the parabigeminal nucleus (PBN) encodes such estimations, combining sensory representations of target location, extrapolated positions of briefly obscured targets, and eye position information. Cui and Malpeli (Cui H, Malpeli JG. J Neurophysiol 89: 3128-3142, 2003) reported that PBN activity for continuously visible tracked targets is determined by retinotopic target position. Here we show that when cats tracked moving, blinking targets the relationship between activity and target position was similar for ON and OFF phases (400 ms for each phase). The dynamic range of activity evoked by virtual targets was 94% of that of real targets for the first 200 ms after target offset and 64% for the next 200 ms. Activity peaked at about the same best target position for both real and virtual targets. PBN encoding of target position takes into account changes in eye position resulting from saccades, even without visual feedback. Since PBN response fields are retinotopically organized, our results suggest that activity foci associated with real and virtual targets at a given target position lie in the same physical location in the PBN, i.e., a retinotopic as well as a rate encoding of virtual-target position. We also confirm that PBN activity is specific to the intended target of a saccade and is predictive of which target will be chosen if two are offered. A Bayesian predictor-corrector model is presented that conceptually explains the differences in the dynamic ranges of PBN neuronal activity evoked during tracking of real and virtual targets.