Ear and eye representation in the frontal cortex, area 8b, of the macaque monkey: an electrophysiological study

Abstract

We evoked both ear and eye movements in area 8b, the rostral area of frontal cortex, in two monkeys. In some sites it was possible to evoke only ear movements or only eye movements; in other locations we evoked both ear and eye movements by varying the intensity of electrical stimulation. The electrically evoked ear movements were forward, or backward, or oblique (upward-forward; upward-backward). In two penetrations the ear movements were bilateral, in the other penetrations they were contralateral. Ipsilateral ear movements were not observed. The evoked eye movements were mainly fixed-vector saccades, contralateral and with an upward orientation of about 45 degrees. If we considered only the sites where the threshold was equal to or lower than 50 microA, the stimulation of this area evoked mainly ear movements. In addition we recorded the electrical activity of 195 neurons. Of these neurons: 74% (145/195) discharged before ear movements (ear cells); 20% (40/195) discharged before ear and eye movements (ear-eye cells); 5% (10/195) discharged only before eye movements (eye cells). Ninety-one percent (132/145) of ear cells presented a preferred direction; 90% (36/40) of ear-eye cells presented a preferred direction for ear movements, and 15% (6/40) presented a preferred direction for eye movements. Eighty-five percent (34/40) of cells did not present a preferred direction for visually guided saccades and were active when the monkey made saccades toward the unlit targets (checking saccades). Our results show that a field of area 8b is related to ear movements and to eye-ear movements. The findings that it is possible to obtain both ear and eye movements with low-intensity currents and that there are cells firing for the two types of movements suggest that area 8b may be involved in the orientation and coordination of both ear and eye. This area might be considered a rostral extension of supplementary eye field (SEF) or a different region. However, based on its distinct functional characteristics and connectivity, it is probably better regarded as a separate field. Regardless, the combination of 8b and SEF may constitute a cortical center for orienting processes.

Oculomotor Areas of the Primate Frontal Lobes: A Transneuronal Transfer of Rabies Virus and [14C]-2-Deoxyglucose Functional Imaging Study

“…The small region with a high concentration of saccaderelated neurons described by these authors is surrounded by a much larger area also containing saccade-related neurons, albeit less frequently, which encompasses the supplementary motor area (SMA), the pre-SMA, and areas of the exposed surface lateral, caudal, and rostral to the SEF (Fujii et al, 1995). Consistent with this, the fact that saccades are evoked in response to electrical stimulation of areas 6 (Shook et al, 1988) and 8B (Bon and Lucchetti, 1994) and the fact that saccade-related cells are encountered in areas 8B (Bon and Lucchetti, 1994) and 9 (Joseph and Barone, 1987), we found additional transneuronally labeled neurons in areas 6, 8B, 9, and corresponding mesial cortical regions.…”

Movement representation in the dorsal and ventral premotor areas of owl monkeys: A microstimulation study

“…The rostral territory, area OMD (Stepniewska et al, 1993a), is architectonically dysgranular, and resembles the cortex denoted as area 8b in other primates (Walker, 1940; see also di Pelligrino and Wise, 1991;Preuss and Goldman-Rakic, 1991;Bon and Lucchetti, 1994). OMD may be less responsive to stimulation than PMD or SMAd, as evidenced by the presence of many unresponsive points in OMD or points that required very strong currents to elicit movements.…”

“…Nevertheless, there is some evidence that both 8b and PMD are involved in eye-movement control in macaques as well. Bon and Lucchetti (1994) have reported eliciting eye and ear movements from area 8b in macaques. Mitz and Godschalk (1989) also elicited eye movements in macaques from sites located rostral to the superior tip of the arcuate sulcus, a region that probably corresponds to area 8b.…”

Neuronal activity in the primate dorsomedial prefrontal cortex contributes to strategic selection of response tactics

“…For example, Petrides proposed that the dorsomedial PFC plays important roles in monitoring multiple events and self-ordering actions (13), although his later study suggested that the dlPFC is also involved in this process (14). Bon and Lucchetti reported that electrical stimulation in area 8b evoked ear or eye movements, and neurons in this region showed activity modulation related to these types of movements (15,16). Human brain-imaging studies identified active areas including the mPFC that were related to the selection of actions and conflict monitoring (17) or to the generation and adjustment of action plans (18).…”