Auditory environmental cells and visual fixation effect in area 8B of macaque monkey

Neuronal Encoding of Self and Others' Head Rotation in the Macaque Dorsal Prefrontal Cortex

Following gaze is a crucial skill, in primates, for understanding where and at what others are looking, and often requires head rotation. The neural basis underlying head rotation are deemed to overlap with the parieto-frontal attention/gaze-shift network. Here, we show that a set of neurons in monkey’s Brodmann area 9/46dr (BA 9/46dr), which is involved in orienting processes and joint attention, becomes active during self head rotation and that the activity of these neurons cannot be accounted for by saccade-related activity (head-rotation neurons). Another set of BA 9/46dr neurons encodes head rotation performed by an observed agent facing the monkey (visually triggered neurons). Among these latter neurons, almost half exhibit the intriguing property of encoding both execution and observation of head rotation (mirror-like neurons). Finally, by means of neuronal tracing techniques, we showed that BA 9/46dr takes part into two distinct networks: a dorso/mesial network, playing a role in spatial head/gaze orientation, and a ventrolateral network, likely involved in processing social stimuli and mirroring others’ head. The overall results of this study provide a new, comprehensive picture of the role of BA 9/46dr in encoding self and others’ head rotation, likely playing a role in head-following behaviors.

Auditory Processing in the Posterior Parietal Cortex

Goal-directed behavior can be characterized as a dynamic link between a sensory stimulus and a motor act. Neural correlates of many of the intermediate events of goal-directed behavior are found in the posterior parietal cortex. Although the parietal cortex’s role in guiding visual behaviors has received considerable attention, relatively little is known about its role in mediating auditory behaviors. Here, the authors review recent studies that have focused on how neurons in the lateral intraparietal area (area LIP) differentially process auditory and visual stimuli. These studies suggest that area LIP contains a modality-dependent representation that is highly dependent on behavioral context.

Evidence for a functional subdivision of Premotor Ear-Eye Field (Area 8B)

The Supplementary Eye Field (SEF) and the Frontal Eye Field (FEF) have been described as participating in gaze shift control. Recent evidence suggests, however, that other areas of the dorsomedial prefrontal cortex also influence gaze shift. Herein, we have investigated electrically evoked ear- and eye movements from the Premotor Ear-Eye Field, or PEEF (area 8B) of macaque monkeys. We stimulated PEEF during spontaneous condition (outside the task performance) and during the execution of a visual fixation task (VFT). In the first case, we functionally identified two regions within the PEEF: a core and a belt. In the core region, stimulation elicited forward ear movements; regarding the evoked eye movements, in some penetrations, stimulation elicited contraversive fixed-vectors with a mean amplitude of 5.14°; while in other penetrations, we observed prevalently contralateral goal-directed eye movements having end-points that fell within 15° in respect to the primary eye position. On the contrary, in the belt region, stimulation elicited backward ear movements; regarding the eye movements, in some penetrations stimulation elicited prevalently contralateral goal-directed eye movements having end-points that fell within 15° in respect to the primary eye position, while in the lateral edge of the investigated region, stimulation elicited contralateral goal-directed eye movements having end-points that fell beyond 15° in respect to the primary eye position. Stimulation during VFT either did not elicit eye movements or evoked saccades of only a few degrees. Finally, even though no head rotation movements were observed during the stimulation period, we viewed a relationship between the duration of stimulation and the neck forces exerted by the monkey's head. We propose an updated vision of the PEEF composed of two functional regions, core and belt, which may be involved in integrating auditory and visual information important to the programming of gaze orienting movements.

Orienting movements in area 9 identified by long-train ICMS

The effect of intracortical microstimulation has been studied in several cortical areas from motor to sensory areas. The frontal pole has received particular attention, and several microstimulation studies have been conducted in the frontal eye field, supplementary eye field, and the premotor ear-eye field, but no microstimulation studies concerning area 9 are currently available in the literature. In the present study, to fill up this gap, electrical microstimulation was applied to area 9 in two macaque monkeys using long-train pulses of 500-700-800 and 1,000 ms, during two different experimental conditions: a spontaneous condition, while the animals were not actively fixating on a visual target, and during a visual fixation task. In these experiments, we identified backward ear movements, goal-directed eye movements, and the development of head forces. Kinematic parameters for ear and eye movements overlapped in the spontaneous condition, but they were different during the visual fixation task. In this condition, ear and eye kinematics have an opposite behavior: movement amplitude, duration, and maximal and mean velocities increase during a visual fixation task for the ear, while they decrease for the eye. Therefore, a top-down visual attention engagement could modify the kinematic parameters for these two effectors. Stimulation with the longest train durations, i.e., 800/1,000 ms, evokes not only the highest eye amplitude, but also a significant development of head forces. In this research article, we propose a new vision of the frontal oculomotor fields, speculating a role for area 9 in the control of goal-directed orienting behaviors and gaze shift control.

Contrasting patterns of cortical input to architectural subdivisions of the area 8 complex: a retrograde tracing study in marmoset monkeys

Contemporary studies recognize 3 distinct cytoarchitectural and functional areas within the Brodmann area 8 complex, in the caudal prefrontal cortex: 8b, 8aD, and 8aV. Here, we report on the quantitative characteristics of the cortical projections to these areas, using injections of fluorescent tracers in marmoset monkeys. Area 8b was distinct from both 8aD and 8aV due to its connections with medial prefrontal, anterior cingulate, superior temporal polysensory, and ventral midline/retrosplenial areas. In contrast, areas 8aD and 8aV received the bulk of the projections from posterior parietal cortex and dorsal midline areas. In the frontal lobe, area 8aV received projections primarily from ventrolateral areas, while both 8aD and 8b received dense inputs from areas on the dorsolateral surface. Whereas area 8aD received the most significant auditory projections, these were relatively sparse, in comparison with those previously reported in macaques. Finally, area 8aV was distinct from both 8aD and 8b by virtue of its widespread input from the extrastriate visual areas. These results are compatible with a homologous organization of the prefrontal cortex in New and Old World monkeys, and suggest significant parallels between the present pathways, revealed by tract-tracing, and networks revealed by functional connectivity analysis in Old World monkeys and humans.

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

The functional roles of the primate posterior medial prefrontal cortex have remained largely unknown. Here, we show that this region participates in the regulation of actions in the presence of multiple response tactics. Monkeys performed a forelimb task in which a visual cue required prompt decision of reaching to a left or a right target. The location of the cue was either ipsilateral (concordant) or contralateral (discordant) to the target. As a result of extensive training, the reaction times for the concordant and discordant trials were indistinguishable, indicating that the monkeys developed tactics to overcome the cue-response conflict. Prefrontal neurons exhibited prominent activity when the concordant and discordant trials were randomly presented, requiring rapid selection of a response tactic (reach toward or away from the cue). The following findings indicate that these neurons are involved in the selection of tactics, rather than the selection of action or monitoring of response conflict: (i) The response period activity of neurons in this region disappeared when the monkeys performed the task under the behavioral condition that required a single tactic alone, whereas the action varied across trials. (ii) The neuronal activity was found in the dorsomedial prefrontal cortex but not in the anterior cingulate cortex that has been implicated for the response conflict monitoring. These results suggest that the medial prefrontal cortex participates in the selection of a response tactic that determines an appropriate action. Furthermore, the observation of dynamic, task-dependent neuronal activity necessitates reconsideration of the conventional concept of cortical motor representation.

Rhesus monkeys' valuation of vocalizations during a free-choice task

Adaptive behavior requires that animals integrate current and past information with their decision-making. One important type of information is auditory-communication signals (i.e., species-specific vocalizations). Here, we tested how rhesus monkeys incorporate the opportunity to listen to different species-specific vocalizations into their decision-making processes. In particular, we tested how monkeys value these vocalizations relative to the opportunity to get a juice reward. To test this hypothesis, monkeys chose one of two targets to get a varying juice reward; at one of those targets, in addition to the juice reward, a vocalization was presented. By titrating the juice amounts at the two targets, we quantified the relationship between the monkeys' juice choices relative to the opportunity to listen to a vocalization. We found that, rhesus were not willing to give up a large juice reward to listen to vocalizations indicating that, relative to a juice reward, listening to vocalizations has a low value.

Auditory-motor and cognitive aspects in area 8B of macaque monkey's frontal cortex: a premotor ear-eye field (PEEF)

In previous reports, we showed the involvement of area 8B neurons in both spontaneous ear and eye movement and in auditory information processing. Audition-related cells responded to complex environmental stimuli, but not to pure tones, and their activity changed during visual fixation as a possible inhibitory expression of the engagement of attention. We observed auditory, auditory-motor and motor cells for both eye and ear movements. This finding suggests that area 8B may be involved in the integration of auditory input with ear and eye motor output. In this paper, we extended these previous studies by examining area 8B activity in relation to auditive orienting behaviour, as well as the ocular orientation (i.e., visual fixation) studied previously. Visual fixation led to inhibition of activity in auditory and auditory-motor cells, which suggests that attention may be involved in both, maintaining the eye position and reducing the response of these cell types. Accordingly, during a given task or natural behaviour, spatial attention seems to affect more than one sensorimotor channel simultaneously. These data add to our understanding of how the neural network, through a two-channel attentive process, accomplishes to switch between two effectors, namely eyes and ears. Considering the functional, anatomical and cytoarchitectonic differences among the frontal eye field (FEF), the supplementary eye field (SEF) and area 8B, we propose to consider area 8B as a separate premotor ear-eye field (PEEF).