The Anterior Cingulate Cortex is Involved in Both Visual Processing and Action Selection

Post by Shireen Parimoo

What's the science?

The prefrontal cortex controls which information from the environment is processed and selects the appropriate response to act on that information. One region in the prefrontal cortex in particular – the anterior cingulate cortex (ACC) – has been implicated in both the processing of visual information as well as motor functioning. Previous research suggests that projections from the ACC to the visual cortex (ACC-VC) and to the superior colliculus (ACC-SC), might be differentially involved in visual processing and motor responding, respectively. However, this prediction has not yet been empirically tested. This week in Nature Communications, Huda and colleagues used optogenetics and two-photon imaging to investigate the contribution of distinct populations of ACC neurons to visuomotor processing.

How did they do it?

Mice were trained on a visually guided task in which a visual stimulus was presented on one side of a screen and mice rotated a trackball to move the stimulus across the screen. In the inward task, mice rotated the trackball to the left or the right in order to move the stimulus toward the center of the screen, whereas in the outward task, the objective was to move the stimuli toward the opposite edge of the screen. Actions were labelled as ipsiversive (toward) or contraversive (away from) relative to activity in the left hemisphere of the brain. Task performance was based on several measures, including the rate of incorrect responses and the timeout rate (i.e. did not move the trackball within the allotted time).

The authors injected viral vectors and performed retrograde and anterograde tracing to identify neuronal projections between the ACC and the superior colliculus and the visual cortex. They then used 2-photon microscopy to examine the activation of these neurons in response to the visual stimulus and during motor responding in the visually guided task. To rule out the involvement of other, unlabeled ACC neurons in task performance, they also trained a type of statistical model — a linear classifier — to predict the action chosen by the mice based on the activation of unlabeled and labelled neurons. Lastly, the authors optogenetically inhibited ACC-SC and ACC-VC neurons while mice performed the task. They recorded task performance in response to the visual stimuli (right or left presentation) and the required action (ipsiversive or contraversive), which allowed them to identify the contribution of these regions to visual and motor processing.

What did they find?

Neurons in the visual cortex projected to the ipsilateral caudal ACC, providing visual information from the contralateral visual hemifield. In turn, neurons in the caudal ACC projected ipsilaterally to the superior colliculus. The caudal ACC received visual information from the ipsilateral hemifield via the corpus callosum, which connected the ACC between the two hemispheres. Importantly, distinct populations of neurons in the ACC were connected to the visual cortex and the superior colliculus. Thus, the anatomical organization of input and output pathways of the ACC did not overlap between the superior colliculus and the visual cortex.

During the visually guided task, optogenetic inhibition of ACC-VC projections increased errors on the task, particularly in response to stimuli presented on the contralateral hemifield. In contrast, inhibiting ACC-SC neurons impaired performance on trials requiring ipsiversive actions, irrespective of which side the stimuli were presented on. Moreover, activation of ACC-SC neurons reliably predicted the selected action better than other ACC neurons, suggesting that ACC projections to the superior colliculus are involved in the selection of ipsiversive motor responses. Overall, these results indicate that the ACC-VC pathway is involved in visual processing whereas the ACC-SC pathway plays a role in action selection.

What's the impact?

This study is the first to demonstrate that distinct populations of neurons in the mouse ACC are involved in the processing of visual information and motor functioning via connections to the visual cortex and the superior colliculus, respectively. These results provide a greater understanding of both the anatomical organization of the ACC as well as its contribution to visual sensorimotor behavior.

Huda et al. Distinct prefrontal top-down circuits differentially modulate sensorimotor behavior. Nature Communications (2020). Access the original scientific publication here.