Saccadic tasks are often used to index aberrations of cognitive function in patient populations, with several neuropsychiatric and neurologic disorders characterized by saccadic dysfunction. The common marmoset (Callithrix jacchus) has received recent attention as an additional primate model for studying the neural basis of these dysfunctions - marmosets are amenable to a host of genetic manipulation techniques and have a lissencephalic cortex, which is well suited for a variety of recording techniques (e.g., calcium imaging, laminar electrophysiology). Because the marmoset cortex is mostly lissencephalic, however, the locations of frontal saccade-related regions (e.g., frontal eye fields (FEF)) are less readily identified than in Old World macaque monkeys. Further, although high quality histology-based atlases do exist for marmosets, identifying these regions based on histology alone is not always accurate, with the cytoarchitectonic boundaries often inconsonant with functional boundaries. As such, there is a need to map the functional location of these regions directly. Task-based functional magnetic resonance imaging (fMRI) is of utility in this regard, allowing for detection of whole-brain signal changes in response to moving stimuli. Here, we conducted task-based fMRI in marmosets at ultra-high field (9.4 T) during a free-viewing visuo-saccadic task. We also conducted the same task in humans at ultra-high field (7 T) to validate that our simple task was indeed evoking the visuo-saccadic circuitry we expected (as defined by a meta-analysis of fMRI saccade studies). In the marmosets, we found that the task evoked a robust visuo-saccadic topology, with visual cortex (V1, V2, V3, V4) activation extending ventrally to MT, MST, FST and dorsally into V6, 19M, 23V. This topology also included putative cingulate eye field (area 32 and 24d), posterior parietal cortex (with strongest activation in lateral intraparietal area (LIP)), and a frontolateral peak in area 8 aV in marmosets, extending into 45, 46, 8aD, 6DR, 8c, 6 aV, 6DC. Overall, these results support the view that marmosets are a promising preclinical modelling species for studying saccadic dysfunction related to neuropsychiatric or neurodegenerative human brain diseases.
In primates, both the dorsal anterior cingulate cortex (dACC) and the dorsolateral prefrontal cortex (dlPFC) are key regions of the frontoparietal cognitive control network. To study the role of the dACC and its communication with the dlPFC in cognitive control, we recorded local field potentials (LFPs) from the dlPFC before and during the reversible deactivation of the dACC, in macaque monkeys engaging in uncued switches between 2 stimulus-response rules, namely prosaccade and antisaccade. Cryogenic dACC deactivation impaired response accuracy during maintenance of-but not the initial switching to-the cognitively demanding antisaccade rule, which coincided with a reduction in task-related theta activity and the correct-error (C-E) difference in dlPFC beta-band power. During both rule switching and maintenance, dACC deactivation prolonged the animals' reaction time and reduced task-related alpha power in the dlPFC. Our findings support a role of the dACC in prefrontal oscillatory activities that are involved the maintenance of a new, challenging task rule.
Electrical microstimulation evokes saccades in posterior parietal cortex of common marmosets.
Ghahremani M, Johnston KD, Ma L, Hayrynen L, Everling S (2019) Neuroimage 116147
The common marmoset (Callithrix jacchus) is a small-bodied New World primate, increasing in prominence as a model animal for neuroscience research. The lissencephalic cortex of this primate species provides substantial advantages for the application of electrophysiological techniques such as high-density and laminar recordings, which have the capacity to advance our understanding of local and laminar cortical circuits and their roles in cognitive and motor functions. This is particularly the case with respect to the oculomotor system, as critical cortical areas of this network such as the frontal eye fields (FEF) and lateral intraparietal area (LIP) lie deep within sulci in macaques. Studies of cytoarchitecture and connectivity have established putative homologies between cortical oculomotor fields in marmoset and macaque, but physiological investigations of these areas, particularly in awake marmosets, have yet to be carried out. Here, we addressed this gap by probing the function of posterior parietal cortex (PPC) of the common marmoset using electrical microstimulation. We implanted two animals with 32-channel Utah arrays at the location of the putative area LIP and applied microstimulation while they viewed a video display and made untrained eye movements. Similar to previous studies in macaques, stimulation evoked fixed-vector and goal-directed saccades, staircase saccades, and eye blinks. These data demonstrate that area LIP of the marmoset plays a role in the regulation of eye movements, provide additional evidence that this area is homologous with that of the macaque, and further establish the marmoset as valuable model for neurophysiological investigations of oculomotor and cognitive control.
Task-based fMRI of a free-viewing visuo-saccadic network in marmosets. Schaeffer DJ, Gilbert KM, Hori Y, Hayrynen LK, Johnston KD, Gati JS, Menon RS, Everling S, (2019) Neuroimage 116147