RESUMEN
Given an instruction regarding which effector to move and what location to move to, simply adding the effector and spatial signals together will not lead to movement selection. For this, a nonlinearity is required. Thresholds, for example, can be used to select a particular response and reject others. Here we consider another useful nonlinearity, a supralinear multiplicative interaction. To help select a motor plan, spatial and effector signals could multiply and thereby amplify each other. Such an amplification could constitute one step within a distributed network involved in response selection, effectively boosting one response while suppressing others. We therefore asked whether effector and spatial signals sum supralinearly for planning eye versus arm movements from the parietal reach region (PRR), the lateral intraparietal area (LIP), the frontal eye field (FEF), and a portion of area 5 (A5) lying just anterior to PRR. Unlike LIP neurons, PRR, FEF, and, to a lesser extent, A5 neurons show a supralinear interaction. Our results suggest that selecting visually guided eye versus arm movements is likely to be mediated by PRR and FEF but not LIP.
Asunto(s)
Lóbulo Frontal/fisiología , Actividad Motora , Corteza Motora/fisiología , Neuronas/fisiología , Desempeño Psicomotor , Movimientos Sacádicos , Animales , Brazo/fisiología , Macaca mulatta , Masculino , Lóbulo Parietal/fisiologíaRESUMEN
To reach for something we see, the brain must integrate the target location with the limb to be used for reaching. Neuronal activity in the parietal reach region (PRR) located in the posterior parietal cortex represents targets for reaching. Does this representation depend on the limb to be used? We found a continuum of limb-dependent and limb-independent responses: some neurons represented targets for movements of either limb, whereas others represented only contralateral-limb targets. Only a few cells represented ipsilateral-limb targets. Furthermore, these representations were not dependent on preferred direction. Additional experiments provide evidence that the PRR is specifically involved in contralateral-limb movements: firing rates are correlated with contralateral- but not ipsilateral-limb reaction times. The current study therefore provides novel evidence that the PRR operates as a limb-dependent stage that lies further along the sensory-motor transformation for visually guided reaching than previously expected.
Asunto(s)
Extremidades/inervación , Neuronas/fisiología , Lóbulo Parietal/citología , Desempeño Psicomotor/fisiología , Potenciales de Acción/fisiología , Animales , Conducta Animal , Lateralidad Funcional , Macaca mulatta , Masculino , Memoria/fisiología , Movimiento/fisiología , Estimulación Luminosa/métodos , Tiempo de Reacción/fisiología , Percepción Espacial/fisiología , Factores de TiempoRESUMEN
To acquire something that we see, visual spatial information must ultimately result in the activation of the appropriate set of muscles. This sensory to motor transformation requires an interaction between information coding target location and information coding which effector will be moved. Activity in the monkey parietal reach region (PRR) reflects both spatial information and the effector (arm or eye) that will be used in an upcoming reach or saccade task. To further elucidate the functional role of PRR in visually guided movement tasks and to obtain evidence that PRR signals are used to drive arm movements, we tested the hypothesis that increased neuronal activity during a preparatory delay period would lead to faster reach reaction times but would not be correlated with saccade reaction times. This proved to be the case only when the type of movement and not the spatial goal of that movement was known in advance. The correlation was strongest in cells that showed significantly more activity on arm reach compared with saccade trials. No significant correlations were found during delay periods in which spatial information was provided in advance. These data support the idea that PRR constitutes a bottleneck in the processing of spatial information for an upcoming arm reach. The lack of a correlation with saccadic reaction time also supports the idea that PRR processing is effector specific, that is, it is involved in specifying targets for arm movements but not targets for eye movements.
Asunto(s)
Atención/fisiología , Movimiento/fisiología , Lóbulo Parietal/fisiología , Desempeño Psicomotor/fisiología , Tiempo de Reacción/fisiología , Animales , Brazo/fisiología , Movimientos Oculares/fisiología , Macaca mulatta , Estimulación Luminosa/métodos , Valor Predictivo de las Pruebas , Factores de TiempoRESUMEN
A localized cluster of neurons in macaque posterior parietal cortex, termed the parietal reach region (PRR), is activated when a reach is planned to a visible or remembered target. To explore the role of PRR in sensorimotor transformations, we tested whether cells would be activated when a reach is planned to an as-yet unspecified goal. Over one-third of PRR cells increased their firing after an instruction to prepare a reach, but not after an instruction to prepare a saccade, when the target of the movement remained unknown. A partially overlapping population (two-thirds of cells) was activated when the monkey was informed of the target location but not the type of movement to be made. Thus a subset of PRR neurons separately code spatial and effector-specific information, consistent with a role in specifying potential motor responses to particular targets.
Asunto(s)
Actividad Motora/fisiología , Lóbulo Parietal/fisiología , Animales , Conducta de Elección , Color , Percepción de Color/fisiología , Electrofisiología , Macaca mulatta , Memoria/fisiología , Neuronas/fisiología , Lóbulo Parietal/citología , Desempeño Psicomotor/fisiología , Tiempo de Reacción , Movimientos Sacádicos/fisiología , Factores de TiempoRESUMEN
When primates reach for an object, they very often direct an eye movement toward the object as well. This pattern of directing both eye and limb movements to the same object appears to be fundamental to eye-hand coordination. We investigated interactions between saccades and reaching movements in a rhesus monkey model system. The amplitude and peak velocity of isolated eye movements are positively correlated with one another. This relationship is called the main sequence. We now report that the main sequence relationship for saccades is changed during coordinated eye and arm movements. In particular, peak eye velocity is approximately 4% faster for the same size saccade when the saccade is accompanied by a coordinated arm movement. Saccade duration is reduced by an equivalent amount. The main sequence relationship is unperturbed when the arm moves simultaneously but in the opposite direction as the eyes, suggesting that eye and arm movements must be tightly coordinated to produce the effect. Candidate areas mediating this interaction include the posterior parietal cortex and the superior colliculus.