The cingulate gyrus is a part of the human brain on the medial aspect of each of the cerebral hemispheres. Along with the parahippocampal gyrus, it makes up the limbic cortex of the brain’s limbic system. As you study the different anatomy topics, you may be feeling a bit overwhelmed, maybe even a little anxious. Ever find yourself fidgeting? Well, that’s your cingulate gyrus helping express your emotional state through gesture, posture and movement.
Recently, the cingulate gyrus has become the subject of many cognitive and neurocognitive studies. It has been implicated in Alzheimer’s disease, anxiety disorders, addiction, depression, bipolar disorder and schizophrenia— just to name a few. In this article, we will begin by exploring the anatomy of the cingulate gyrus. We will then explore the different regions and their functions, and finally, discuss some of the clinical aspects of the region as it relates to neuropsychiatric disease.
The cingulate gyrus commences below the rostrum of the corpus callosum. Here, it spans the width of the lamina terminalis to the anterior commissure, curves around in front of the genu of the corpus callosum, travels along the superior surface of the body, and terminates at a narrow isthmus behind the splenium. The isthmus of the cingulate gyrus is continuous inferiorly with the parahippocampal gyrus in the temporal lobe of the human brain.
The inferior limit of the cingulate gyrus is defined at the callosal sulcus, and superiorly, it is bounded by the inferior bank of the cingulate sulcus. In both humans and nonhuman primates, the cingulate cortex consists of the cingulate gyrus and the cortical matter in the overlaying cingulate sulcus.
In 1909, Brodmann defined a pre-cingulate region (areas 25, 24 and 32; anterior cingulate cortex) and a post-cingulate region (areas 23 and 31; posterior cingulate cortex) with the clearest distinction between the two being their cortical layer IV neurons. In the anterior segments of the cingulate surface, the cortex is very thin, and lacks a granular layer IV. Conversely, the posterior cingulate cortex is either dysgranular or has a pronounced and distinct accumulation of granular cells.
More recently, it has become clear that in fact Brodmann’s anterior and posterior cingulate cortices are not uniform in cytoarchitecture, connections, function or psychiatric disease responses, and that this model is too simplistic. In 2004, Vogt et al introduced a new neurobiological model defining four segregated areas of the cingulate cortex:
- anterior cingulate
- posterior cingulate
- retrosplenial cortices
These functionally distinct regions are collections of areas with similar cytoarchitecture and a common function, and will be explored further in the following sections.
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.
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.
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.
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.
The pericallosal artery, which is a continuation of the anterior cerebral artery, distributes blood to most of the rostrum of the corpus callosum. It gives off many small cortical branches to the medial surfaces of the cerebral hemispheres, including the cingulate gyrus. Frontal cortical branches of the pericallosal artery supply the gyral surface, or cortical branches from the callosomarginal artery, when it is present. The callosomarginal artery runs within the cingulate sulcus.
When present, the internal paracentral artery, a branch of the callosomarginal artery, supplies the paracentral lobule and the cingulate gyrus just underneath of it. The precuneal artery, a branch of the pericallosal artery, supplies the precuneus and posterior cingulate cortex. The pericallosal artery may anastomose with the precuneal artery and the parieto-occipital artery (from the posterior cerebral artery). It may also give off either the parieto-occipital or the inferior parietal artery as cortical branches to distribute to the cortical matter just above the splenium of the corpus callosum. The isthmus of the cingulate gyrus is frequently supplied by an anastomosis of the splenial artery with terminal branches of the pericallosal artery.