Cingulate gyrus

Anterior cingulate cortex

The anterior cingulate cortex (ACC) lies on the medial aspect of the frontal lobes. The pyramidal cells here are large, branched, and very spinous when compared to the posterior cingulate gyrus, as well as other visual, somatosensory and motor cortices. This region can be further divided into a subgenual ACC (area 25 and ventral portions of 24 and 32) and a perigenual ACC (areas 32 and 24).

Anatomically, the subgenual ACC is located beneath the genu as its name would suggest, whereas the perigenual ACC is located near the genu of the corpus callosum. In some of the literature, the perigenual cingulate and subgenual areas are termed the “affective subdivision” of the ACC, as they maintain strong connections with limbic and paralimbic structures.

Midcingulate cortex

The midcingulate cortex (MCC; sometimes referred to as the dorsal ACC), includes posterior parts of Brodmann areas 24 and 32 as well as the cingulate motor area (CMA). Anatomically, the caudal limit of the MCC comes before the marginal sulcus adjacent to the precuneus and the paracentral lobule.  

Based on anatomic criteria such as cytoarchitecture, receptor mapping, and connections, the MCC can be further divided into two sub-areas: dorsal midcingulate cortex (dMCC; areas 24, 32 and 33) and a region on the surface of the cingulate gyrus. The dMCC is located in the sulcal cortex and extends onto the superior cingulate gyrus adjacent to the lateral prefrontal cortex and pre-supplementary motor areas. The gyral surface has large layer Vb neurons that project to the spinal cord and the supplementary and primary motor and limbic cortices. Interestingly, these neurons fire according to the changing reward properties of particular behaviours.

The cingulate motor area (CMA) is one of the higher order motor areas in the cortex. It is located in the cingulate sulcus adjacent to the primary and supplementary motor areas of the frontal lobe. The CMA has rostral and caudal segments, each with a unique afferent input as well as neurons with differing response properties. For instance, while both the caudal and rostral CMAs send neural information to the striatum, their projections overlap with different areas of the cortex. The caudal CMA projects to the same location in the striatum as the primary motor cortex, while the rostral CMA’s projections overlap with those from pre-supplementary motor areas.

Posterior cingulate cortex

The posterior cingulate cortex (PCC) is comprised of Brodmann areas 23 and 31. These areas have well-differentiated layers IIIc, IV, and Va. Anatomically, the PCC is bounded superiorly by the cingulate sulcus, inferiorly by the corpus callosum, posteriorly by the parieto-occipital sulcus and anteriorly by Brodmann area 24 in the midcingulate region.

Within the PCC, the retrosplenial cortex (RSC; areas 29 and 30) has been defined as separate from other parts of the region. In monkey studies, the RSC maintains reciprocal connections with the hippocampal formation, parahippocampal region, and anterior and lateral dorsal thalamic nuclei.

Anterior cingulate cortex

Broadly speaking, the ACC is involved in autonomic and endocrine responses to emotion, and memory storage. The subgenual ACC in particular, is likely engaged in regulating endocrine function and expressing autonomic states through its projections with the nucleus of the solitary tract and dorsal motor nucleus of the vagus nerve (i.e.: autonomic brainstem nuclei). It also has extensive connections with the:

• amygdala, a region of the brain highly involved in emotional responses
• periaqueductal gray, a primary site for top-down pain modulation
• medio-dorsal and anterior thalamic nuclei, which are thought to be involved in attention, learning, and memory functions.

Midcingulate cortex

The MCC is recruited when we make predictions about the outcome of behaviour, and helps to execute said behaviour through cingulo-spinal projections that arise in the CMA.

Therefore, along with its strong connections to the dorsolateral prefrontal cortex, supplementary motor areas, parietal cortices and the spinal cord, the MCC is thought to be involved in processing information around reward-based decision making and cognitive activity associated with intentional motor control.

The presence of the CMA in the MCC is further evidence in support of the functional dichotomy discussed above. The CMA receives neural signals from the limbic structures, prefrontal cortex and motor regions, and sends output projections to the primary and secondary motor areas and other motor structures in the brainstem and spinal cord. Based on existing evidence of structural and functional connectivity, the CMA appears to be involved in the processing of information around internal and external states and subsequently selecting voluntary actions in accordance with these conditions.

Posterior cingulate cortex

Broadly speaking, the PCC is involved in a topokinetic memory circuit, with a primary function in visuospatial orientation. The ventral PCC appears to be highly integrated within the brain’s ‘default mode network’ (a system in the brain that is remains active when we do not pay attention to external stimuli), and is thought to be involved in processes of internally directed cognition such as memory retrieval, planning, and processing spatial information. It is also hypothesized to be involved in self-monitoring and assessment of events for self-relevance (via interactions with the ACC). The dorsal PCC on the other hand, is intimately connected with the premotor, dorsal visual, and orbitofrontal regions of the brain and is involved in orientating one’s body in a visual space.

Retrosplenial cortex

In human neuropsychological studies, the RSC has been implicated in spatial navigation, autobiographical memory retrieval and imagination. Consequently, many neurological disorders that impair memory are associated with pathology in this region.