Information flows from the perirhinal and parahippocampal cortex to the hippocampus.
Connections exist within and among these regions.
Flow of Information:
ERC = Entorhinal Cortex
PRC = Perirhinal Cortex
PHC = Parahippocampal Cortex
Neocortical Areas
SUBFIELDS OF HIPPOCAMPUS
The hippocampus is subdivided based on neuron structure (cytoarchitecture).
Views of subdivisions include coronal and axial (top-down) views.
Key divisions:
HEAD
TAIL
HIPPOCAMPUS AS AN INDEX
Conceptual understanding of the hippocampus as an indexing region.
Briefly outlined connections with other brain regions.
Theoretical implications discuss memory retrieval and formations based on various intervals.
MEMORY INDEX THEORY
Describes the relationship between neocortical and hippocampal activity:
A: Initial State
Specific neocortical patterns activated by experience project to hippocampus activating unique synapses.
B: Memory Storage
Strengthened connections formed among activated hippocampal synapses.
C: Retrieval Process
A subset of input can reactivate hippocampal representation.
D: Activation Loop
Hippocampal output activates full neocortical pattern.
Reference: Teyler & Rudy (2007)
COMPUTATIONS IN THE HIPPOCAMPUS
Different hippocampal subfields perform specific computational tasks:
Pattern Separation:
Distinguishes similar overlapping representations.
Pattern Completion:
Makes overlapping representations more similar.
Subfields CA3/DG support Pattern Separation; CA1 supports Pattern Completion.
NEURAL EVIDENCE FOR DIFFERENT COMPUTATIONS IN THE HIPPOCAMPUS
Study of objects in repeated trials categorized as either identical or similar lures.
Repetition Suppression:
Decreased activity in a brain region signifying identical treatment of trials.
PATTERN DISTINCTION IN CA3/DG AND CA1
CA3/DG is capable of distinguishing similar lures indicative of Pattern Separation while CA1 struggles, leaning towards Pattern Completion.
THE HIPPOCAMPUS AS A COGNITIVE MAP
Foundational theories by O’Keefe (1971) and Nadel & O’Keefe (1978) suggest:
The hippocampus provides a spatiotemporal context for memories, lending it content-driven characteristics rather than merely being an index.
COGNITIVE MAP STUDY
Maguire et al. (1998) conducted navigation tasks in a VR city:
Independent Variable:
Group 1 - Feely explore (cognitive map)
Group 2 - Follow arrows (no cognitive map)
Findings indicate the right hippocampus is crucial for successful navigation, demonstrating a right-hemisphere bias towards space.
LONDON TAXI DRIVER STUDY
Maguire et al. (2000) investigated volumetric differences in the hippocampus:
Independent Variables:
London Taxi Drivers
Non-Taxi Drivers
Dependent Variable:
Volume of hippocampus and amount of gray matter.
Study suggests anterior versus posterior hippocampal functionality differs, with taxi drivers exhibiting a larger posterior hippocampus but smaller anterior hippocampus.
Neurogenesis implications were discussed regarding new neurons.
LONDON TAXI DRIVER STUDY: IMPACT OF EXPERIENCE
Findings revealed:
Enhanced hippocampal volume correlates with duration of experience driving in London.
Importance of prior hippocampal size was noted, with no significant volume differences found prior to taxi driving initiation.
Taxi drivers exhibit a larger posterior hippocampus compared to bus drivers.
HIPPOCAMPUS AS A MAP OF SOCIAL SPACE
Tavares et al. (2015) describe how the hippocampus supports memory navigation through abstract routes:
Concepts of social distance, power, and affiliation explored in relation to memory networks.
Experimental findings indicated greater left hippocampal activity as social distance increased.
HIPPOCAMPUS & RELATIONAL MEMORY
Davachi (2006) discussed the integration of disparate elements across space and time in relational memory (example: visualizing a bowl of fruit by linking spatial configuration with object features).
MEMORY FORMATION IN THE HIPPOCAMPUS
Kim (2011) conducted a meta-analysis of 74 studies:
Findings support that remembered items show greater recruitment of bilateral hippocampi compared to forgotten items.
Neuropsychological evidence suggests damage leads to anterograde amnesia, affecting new memory formation.
HIPPOCAMPUS & RETRIEVAL
Addis et al. (2011) demonstrated greater hippocampal recruitment when recalling autobiographical memories compared to control tasks indicating key roles in memory retrieval.
Neuropsychological evidence shows retrograde amnesia occurs due to hippocampal damage impacting retrieved episodic memories.
HIPPOCAMPUS & MEMORY RECOLLECTION
Investigated by Diana et al. (2007):
Dissimilarity between recollection and familiarity knowledge, with distinctions made between the hippocampus (binding items and contexts) and other areas responsible for item and context.
Structures involved:
Perirhinal cortex: Items
Entorhinal cortex: Context
Parahippocampal cortex: Contextual elements
MEMORY IN OTHER BRAIN AREAS
Uncapher & Rugg (2009) proposed many areas outside the hippocampus aid memory formation including posterior parietal and prefrontal cortices.
Findings: Remembered items show greater engagement than forgotten ones in a meta-analysis of 90 different studies.
OTHER BRAIN AREAS & EMOTIONAL MEMORY
Dahlgren, Ferris, & Hamann (2020) completed a meta-analysis elucidating multiple regions involved in emotional memory encoding and retrieval including prefrontal cortex, occipital cortex, amygdala, etc.
COMPONENT PROCESSING FRAMEWORK
Moscovitch (1992) introduced a theory where various brain regions support different components of memory:
Hippocampus: Encoding/Ecphory
Frontal Lobes: Control over memory
Neocortex: Perceptual/Semantic aspects
Basal Ganglia: Motor-based facets
LARGE-SCALE BRAIN NETWORKS
Research by Buckner, Andrews-Hanna, and Schacter (2008) explored brain regions that activate more during rest than active tasks, indicating distinct memory processes.
PROCESS SPECIFIC ALLIANCES (PSA)
Tasks create flexible, temporary alliances of brain regions, detailing how different areas interact for cognitive processes.
Specific examples include:
VLPFC-Hippocampal interactions: Memory encoding
VLPFC-Amygdala interactions: Emotional regulation
SUMMARY OF HIPPOCAMPUS FUNCTIONS
Memory is supported by activity patterns that include the hippocampus along with other cortical regions.
Multiple theories exist regarding the hippocampus functions: