The<unk>  is highly connected and one of the most metabolically active regions in the brain, but there is no consensus as to its cognitive role. Cerebral blood flow and metabolic rate in the<unk>  are approximately 40% higher than average across the brain. The high functional connectivity of the<unk> , signifies extensive intrinsic connectivity networks (networks of brain regions involved in a range of tasks that share common spatio-temporal patterns of activity). Emotion and memory The<unk>  has been linked by lesion studies to spatial memory, configural learning, and maintenance of discriminative avoidance learning. More recently the<unk>  was shown to display intense activity when autobiographical memories (such as those concerning friends and family) are recalled successfully. In a study involving autobiographical recollection, the caudal part of the left<unk>  was the only brain structure highly active in all subjects. Furthermore, the<unk>  does not show this same activation during attempted but unsuccessful retrieval, implying an important role in successful memory retrieval (see below: Alzheimer’s Disease). The<unk>  has also been firmly linked to emotional salience. Thus, it has been hypothesized that the emotional importance of autobiographical memories may contribute to the strength and consistency of activity in the<unk>  upon successful recollection of these memories. The<unk>  is significantly bilaterally activated by emotional stimuli, independent of valence (positive or negative). This is in contrast to other structures in the limbic system, such as the amygdala, which are thought to respond disproportionately to negative stimuli, or the left frontal pole, which activated only in response to positive stimuli. These results support the hypothesis that the<unk>  mediates interactions between emotion and memory. Intrinsic control networks The<unk>  exhibits connectivity with a wide range of intrinsic control networks. Its most widely known role is as a central node in the default mode network (DMN). The default mode network (and the<unk>  is highly reactive and quickly deactivates during tasks with externally directed, or presently centered, attention (such as working memory or meditation). Conversely, the DMN is active when attention is internally directed (during episodic memory retrieval, planning, and daydreaming). A failure of the DMN to deactivate at proper times is associated with poor cognitive function, thereby indicating its importance in attention. In addition to the default mode network, the<unk>  is also involved in the dorsal attention network (a top-down control of visual attention and eye movement) and the frontoparietal control network (involved in executive motor control). Furthermore, fMRI studies have shown that the<unk>  activates during visual tasks when some form of monetary incentive is involved, essentially functioning as a neural interface between motivation-related areas and top-down control of visual attention. The relationship between these networks within the<unk>  is not clearly understood. When activity increases in the dorsal attention network and the frontoparietal control network, it must simultaneously decrease in the DMN in a closely correlated way. This anti-correlated pattern is indicative of the various differences and importance of subregions in the<unk> . Considering the relation of the<unk>  with the DMN, with suppressed posterior<unk>  activity favoring low cognitive introspection and higher external attention and increased activity indicating memory retrieval and planning, it has been hypothesized that this brain region is heavily involved in noticing internal and external changes and in facilitating novel behavior or thought in response. High activity, then, would indicate continued operation with the current cognitive set, while lower activity would indicate exploration, flexibility and renewed learning. An alternative hypothesis is focused more on the difference between the dorsal and ventral subregions and takes into consideration their functional separation. In this model, the<unk>  is hypothesized to take a chief regulatory role in focusing internal and external attention. Mounting evidence that the<unk>  is involved in both integrating memories of experiences and initiating a signal to change behavioral strategies supports this hypothesis. Under this model, the<unk>  plays a crucial role in controlling state of arousal, the breadth of focus and the internal or external focus of attention. This hypothesis emphasizes the<unk>  as a dynamic network, rather than a fixed and unchanging structure. While both of the hypotheses are the result of scientific studies, the role of the<unk>  is still not well understood and there remains much work to be done to investigate the extent of their veracity. Meditation From neuroimaging studies and subjective descriptions, the<unk>  has been found to be activated during self-related thinking and deactivated during meditation. Using generative topographic mapping, it was further found that undistracted, effortless mind wandering corresponds with<unk>  deactivation, whereas distracted and controlled awareness corresponds with<unk>  activation. These results track closely with findings about the role of the<unk>  in the DMN.
Posterior cingulate cortex
Periventricular nucleus
Piriform cortex
Fusiform body area
Retrosplenial cortex
Posterior parietal cortex
Arcuate nucleus 
Postrhinal cortex