Posterior parietal cortex contains a command apparatus for hand movements

Abstract

Mountcastle and colleagues proposed that the posterior parietal cortex contains a "command apparatus" for the operation of the hand in immediate extrapersonal space [Mountcastle et al. (1975) J Neurophysiol 38(4):871-908]. Here we provide three lines of converging evidence that a lateral region within area 5 has corticospinal neurons that are directly linked to the control of hand movements. First, electrical stimulation in a lateral region of area 5 evokes finger and wrist movements. Second, corticospinal neurons in the same region of area 5 terminate at spinal locations that contain last-order interneurons that innervate hand motoneurons. Third, this lateral region of area 5 contains many neurons that make disynaptic connections with hand motoneurons. The disynaptic input to motoneurons from this portion of area 5 is as direct and prominent as that from any of the premotor areas in the frontal lobe. Thus, our results establish that a region within area 5 contains a motor area with corticospinal neurons that could function as a command apparatus for operation of the hand.motor control | motor systems | movement control | cerebral cortex I n a landmark paper, Mountcastle and his colleagues proposed that the posterior parietal cortex contains "a command apparatus for operation of the limbs, hands and eyes within immediate extrapersonal space" (1, p. 871). This hypothesis was based, in part, on the observation that some neurons in areas 5 and 7 were activated not by sensory stimuli but by the animal reaching for or manipulating a desired object. These "arm-projection" and "handmanipulation" neurons were not active during other movements in which the same muscles were used. Instead, their activity was "conditional in nature" and dependent on the animal's intention to explore the immediate surrounding space manually.The development of the command hypothesis led Mountcastle and colleagues to reinterpret some of the consequences of parietal lobe damage: "We propose that several of the abnormalities of function that occur in humans and in monkeys after lesions of the parietal lobe can be understood as deficits of volition, of the will to explore with hand and eye the contralateral half-field of space ... " (1, p. 905) and "We infer that these defects reflect the loss of a particular source of commands for movement" (1, p. 901).The command hypothesis represented a fundamental paradigm shift in concepts about the function of the posterior parietal cortex. The prevailing view at the time was that the cortical areas within the posterior parietal cortex were part of the "association cortex." These cortical regions were thought to construct higher-order sensory representations based on input from primary and secondary sensory areas. In addition, they were thought to play a role in the integration of information from multiple sensory modalities. The results of this integration then could be used by other cortical areas and subcortical motor centers to guide movement. The command hypothesis was novel in viewing the posterior p...

Differential innervation within a transverse plane of spinal gray matter by sensorimotor cortices, with special reference to the somatosensory cortices

“…The cortical areas in which intracortical microstimulation generated body movement project to the dorsal horn (Asante & Martin, ; Rathelot et al, ). In addition, CS neurons in these areas make disynaptic connections with motoneurons (Rathelot et al, ). These results suggest that CS neurons sending their axons to the dorsal horn also make a fairly direct contribution to movement.…”

Neural Basis of Touch and Proprioception in Primate Cortex

“…Area 5L projects ipsilaterally and bilaterally to other parts of area 5, area 7, LPC, motor cortices, and superior temporal gyrus (164). Neurons in area 5L have been shown to encode texture and object shape (2, 171) but lesions in this area have only modest effects on animals’ ability to discriminate passively presented textures (254, 270), consistent with its putative role in the planning of grasping and other manual behaviors that require information about shape and texture (124, 128, 129, 298). During a grasp, neurons in area 5L respond strongly during the approach, their response peaks during the grasp, and then drops during the lift, with a majority inhibited during hold (124).…”

Response Hand and Motor Set Differentially Modulate the Connectivity of Brain Pathways During Simple Uni-manual Motor Behavior

“…The thalamus in addition to its role as an attention relay (Saalmann & Kastner, 2011), helps regulate and coordinate activity across motor regions (Ahissar & Oram, 2013), suggesting that the M1 ←→ thalamus sub-network is an important motor-attention functional loop. Both the SMA and the parietal cortex have been implicated in command-related signaling of basic hand movements (Rathelot, Dum, & Strick, 2017), and their responses (Sale et al, 2017) and inter-regional interactions are known to underpin motor learning. As Figure 4 and Figure X demonstrates, the combination of responding with the dominant effector while establishing a motor set (periodic condition) induces greater uFC and dFC in these sub-networks, implying that the condition evokes representations of handedness.…”