Organization of the posterior parietal cortex in galagos: I. Functional zones identified by microstimulation

Abstract

We used half-second trains of intracortical microstimulation to study the functional organization of the posterior parietal cortex (PPC) in prosimian galagos. These trains of current pulses evoked meaningful behaviors from the anterior, but not posterior, half of PPC. Stimulation of dorsal PPC caused contralateral forelimb movements, including defensive, hand-to-mouth, and reaching movements. Defensive and hand-to-mouth movement territories overlapped, although hand-to-mouth movements were usually evoked from more rostrolateral sites than defensive movements. Reaching movement sites were typically more caudal than defensive or hand-to-mouth movement sites. Stimulation of the most medial PPC sites evoked complex movements of forelimbs and hindlimbs. Ventral PPC commonly represented defensive face movements. Similar defensive movements, with the addition of widely opening the mouth to expose the teeth, were elicited from a small area in front of the PPC defensive face zone. Sometimes defensive face movements occurred with forelimb movements. Thus, subregions of PPC relate to different ethologically relevant categories of behavior. Most movements were initiated within 33–100 msec after stimulus onset. Face, eye blink, and ear movements were generally less delayed than forelimb movements. The present results in galagos, together with those obtained from macaque monkeys by Graziano and coworkers, suggest that the functional involvement of the PPC in specific types of sensorimotor behavior evolved early in the course of primate evolution and that networks for complex movements involving motor and posterior parietal areas are characteristic of all primate brains.

Optical imaging in galagos reveals parietal–frontal circuits underlying motor behavior

“…As expected from the somatotopy of the motor maps in M1 and PM cortex (19), movement zones in PPC that involve the face have more connections in the lateral zones of M1-PM cortex than in the medial movement zones that involve the hand and forelimb (Fig. 1).…”

“…1). Longtrain electrical stimulation also evoked similar complex movements from M1 and PM cortex, and zones for specific classes of matching movements were aligned in a somatotopic pattern that paralleled those zones of PPC (19).…”

“…Electrical stimulation consistently produced movements in the rostral onehalf of PPC (PPCr) and not in its caudal one-half. Movements were evoked from the cortex up to the estimated border of areas 1 and 2, and some effective sites may have been slightly across this border (18,19). By carefully monitoring multiple physiological parameters, including EEG (Materials and Methods), we were able to maintain stable levels of anesthesia.…”

“…In addition, they have identified matching zones in PPC and M1-PM regions where similar defensive movements of the arm and face can be evoked (16,17). Our more recent studies with long-train stimulation have identified a series of functional zones in PPC of prosimian galagos (18,19). These PPC movement zones are preferentially interconnected with functionally matched zones in PM and motor cortex (20).…”

Complex Movement Topography and Extrinsic Space Representation in the Rat Forelimb Motor Cortex as Defined by Long-Duration Intracortical Microstimulation

“…This repertoire of ethological movements was more restricted than that observed in primates (Graziano et al, 2002a;Stepniewska et al, 2009;Gharbawie et al, 2011), in part reflecting the more limited forelimb movement repertoire of the rat. However, the ICMS-evoked repertoire in the rat seems to be richer than those found in mice (Harrison et al, 2012).…”