Retroplenary area: features and functions
The retroplenial area is an area of the brain linked to episodic and contextual memory, navigation or the imagination of future events and scenes. Its importance lies in being a necessary part of a set of regions involved in the management of brain activity when the mind and body are at rest.
In this article we explain you what the retro-splenial area consists of, where it is located, what are the main functions it performs and what kind of disorders can arise if this region of the brain is damaged.
Retroplenial area: definition and neuroanatomical location
The retro-splenial area or cortex (RSC) is a region of the brain located at the bottom of the cingulate gyrus , extending around the corpus callosum, a structure that connects the two brain hemispheres. It comprises Brodmann’s areas 29 and 30 and together with the precuneo and posterior cingulate forms a posterior nucleus which is sometimes referred to as the “posteromedial cortex”.
This brain region is connected to the posterior cingulate cortex (PCC) and has strong connections to the pre-genital and sub-genital anterior cingulate cortex. The CCC and RCC are part of the brain network by default, a set of brain areas that are activated (up to 20% above other regions) when the mind wanders and is at rest.
Animal studies have revealed that the retro-splenial area would have reciprocal connections with these three regions: the hippocampus, the parahippocampal gyrus and certain nuclei of the thalamus . Traumatic damage and pathologies associated with these areas of the brain would be involved in many amnestic syndromes.
Other notable connections between the SRC and different areas of the prefrontal cortex (specifically Brodmann Areas 46, 9, 10 and 11) have also been described, providing an indirect route for the hippocampus to connect to the dorsolateral prefrontal cortex, and vice versa.
Functions
Studies have determined that the retroplenial area has a significant role in spatial and episodic (or contextual) memory, navigation, imagination of future events and scene processing . This brain region would also be involved in processes involving the recognition of permanent and non-mobile environmental landmarks, as well as spatial judgments.
Below we will look in more detail at some of the main tasks in which the retro-splenial area is involved:
Navigation, spatial and contextual memory
Functional magnetic resonance studies have shown that activity in the retro-splenial area is modulated by a variety of processes, ranging from basic speech production and understanding to motivation and pain. However, its involvement in navigation and spatial memory tasks seems to be very clear , and most brain imaging studies confirm this.
In a recent meta-analysis, the retro-splenial area showed significant activation during the recovery of autobiographical information, and more specifically in recent versus remote experiences, although it seems to be activated when we remember any kind of experience in which we are the protagonists, regardless of whether the tone is more neutral or emotional.
On the other hand, it has also been observed that the retro-splenary area is involved in space navigation tasks. These include the passive display of navigation images, mental navigation and interactive navigation in virtual reality environments .
In addition, activity has also been seen during the learning of new and newly learned environments, as well as in very familiar settings. In fact, it seems difficult to find any navigation or topographic memory task in which this region is not activated.
In relation to virtual environments, a study using a virtual reality simulation of central London found that activity in the retro-splenary area increased when topographic representations had to be updated, integrated or manipulated for route planning or when new topographic information had to be acquired. Therefore, it seems that the activity of this brain region would vary according to the specific circumstances and priorities.
Finally, with regard to the relationship of the retro-splenial area and the processing of scenes, it has been suggested that this region could process relationships relevant to the scene , such as those arising from objects and their context. In several studies it has been determined that this area is activated by seeing objects strongly associated with a specific context, and not the other way around (when such association is weak).
The imagination of future events
In recent years, new research has emerged in the field of memory based on the following premises: first, the fact that patients with bilateral damage to the hippocampus not only cannot remember past experiences, but also have difficulty imagining fictional and future experiences; and second, the discovery that remembering past experiences activates many brain regions that are also activated by imagining a plausible personal future and fictional experiences.
Another meta-analysis involving several studies on this issue confirmed that the retroplenial area is part of a common “core network” that maintains a variety of cognitive functions. This network would support the construction of “scenes” (the process of generating and mentally maintaining a complex and coherent image or event), hence it is essential in autobiographical memory, navigation or thinking about the future .
The link between memory and navigation with the imagination of future events places this brain region in a crucial position to understand these cognitive processes. A recent functional MRI study examined brain activation during recovery from autobiographical events, movie episodes, and real news clippings, as well as imagined events of all three types. The results concluded that there was greater activation upon recovery from real events.
Related disorders
Injuries in the retroplenial area may produce an amnestic syndrome characterized by antegrade loss (inability to store new events) of verbal and non-verbal memories, accompanied by mild retrograde amnesia (inability to remember events that occurred before the injury). The extent of retrograde amnesia varies from less than 1 year to 10 years.
In turn, damage to the right portion of the retro-splenial area can generate a selective deficit in spatial orientation and an amnesia of topographic features : the subject can recognize familiar buildings and landscapes, but loses the positional relationship between two known sites. This occurs because it is possible that this area plays an important role in the codification of novel sites and their relationships.
In most cases, patients can recognize landmarks in their neighborhood, for example, but cannot effectively navigate in familiar environments, indicating that they are not able to understand directional information from signals at certain landmarks.
Damage in the retro-splenial area can also compromise learning in new environments . Subjects with damaged hippocampus also show difficulties in navigating familiar and new environments, but unlike people with injuries in the retro-splenial area, they are generally able to orient themselves in such environments and retain their sense of direction.
Bibliographic references:
- Clark, D. L., Boutros, N. N., & Méndez, M. F. (2012). The brain and behaviour: neuroanatomy for psychologists. Modern Handbook.
- Maddock, R. J. (1999). The retrosplenial cortex and emotion: new insights from functional neuroimaging of the human brain. Trends in neurosciences, 22(7), 310 – 316.
- Zola-Morgan, S., & Squire, L. R. (1993). Neuroanatomy of memory. Annual review of neuroscience, 16(1), 547 – 563.