Conscious Experience and Episodic Memory: Hippocampus at the Crossroads

Abstract

If an instance of conscious experience of the seemingly objective world around us could be regarded as a newly formed event memory, much as an instance of mental imagery has the content of a retrieved event memory, and if, therefore, the stream of conscious experience could be seen as evidence for ongoing formation of event memories that are linked into episodic memory sequences, then unitary conscious experience could be defined as a symbolic representation of the pattern of hippocampal neuronal firing that encodes an event memory – a theoretical stance that may shed light into the mind-body and binding problems in consciousness research. Exceedingly detailed symbols that describe patterns of activity rapidly self-organizing, at each cycle of the θ rhythm, in the hippocampus are instances of unitary conscious experience that jointly constitute the stream of consciousness. Integrating object information (derived from the ventral visual stream and orbitofrontal cortex) with contextual emotional information (from the anterior insula) and spatial environmental information (from the dorsal visual stream), the hippocampus rapidly forms event codes that have the informational content of objects embedded in an emotional and spatiotemporally extending context. Event codes, formed in the CA3-dentate network for the purpose of their memorization, are not only contextualized but also allocentric representations, similarly to conscious experiences of events and objects situated in a seemingly objective and observer-independent framework of phenomenal space and time. Conscious perception, creating the spatially and temporally extending world that we perceive around us, is likely to be evolutionarily related to more fleeting and seemingly internal forms of conscious experience, such as autobiographical memory recall, mental imagery, including goal anticipation, and to other forms of externalized conscious experience, namely dreaming and hallucinations; and evidence pointing to an important contribution of the hippocampus to these conscious phenomena will be reviewed.

Reward-Based Spatial Learning in Unmedicated Adults With Obsessive-Compulsive Disorder

“…orbitofrontal cortex and ventral striatum), these mesolimbic regions comprise a reward processing system(3) that allows us to anticipate, respond to, and learn from reward outcomes in quotidian life. Whereas ventral/anterior hippocampus is intrinsically connected to ventral striatum(4), processes reward-related information, and is preferentially involved in anxiety(5), dorsal/posterior hippocampus preferentially processes spatial information(6). Using an ecologically valid task of reward-based spatial learning adapted from animal research, we sought to identify functional impairments in mesolimbic and ventral striatal circuitry that may contribute to OCD behaviors.…”

“…Twenty-one of these individuals were treatment naïve and 12 were off psychotropic medications for at least 12 weeks. Given findings of functional deficits in reward processing circuits(9) and compensatory hippocampal engagement during other learning tasks(22) in OCD, together with the differential roles of posterior and anterior hippocampus in processing spatial and reward information, respectively(6), we made the following hypotheses. First, we hypothesized that whereas both groups would engage tempoparietal areas while navigating the maze, OCD participants would over-engage posterior hippocampus during spatial learning.…”

Do not get lost in translation: The role of egocentric heading in spatial orientation

“…These preliminary findings are in value in supporting the role of the so-called mental frame syncing in the spatial processing [21,22], namely a cognitive process that permits an effective retrieval by the synchronization of the two types of allocentric representations [23], the viewpoint-independent representation (i.e., including object-to-object information) and the allocentric viewpoint-dependent representation (i.e., including information about egocentric current heading). Some evidence has shown that two regions within the hippocampus are specifically involved in the processing of allocentric information [24,25].…”

“…The second region consists of the neurons in CA1, which receives inputs from CA3 via Schaffer's collaterals and encodes allocentric representations involving only abstract, object-to-object information. This is what Behrendt calls allocentric viewpoint-independent representation [23].…”

“…One is region CA3, which receives inputs from the entorhinal cortex and encodes an allocentric representation of the spatial scene toward which the individual orients. This is what Behrendt calls the allocentric viewpoint-dependent representation [23]. The second region consists of the neurons in CA1, which receives inputs from CA3 via Schaffer's collaterals and encodes allocentric representations involving only abstract, object-to-object information.…”