This section links to atlas resources relevant to Hippocampus. [1]
The hippocampus is a seahorse-shaped structure located in the medial temporal lobe of the brain, forming a critical part of the limbic system. It plays essential roles in memory consolidation, spatial navigation, and emotional processing. The hippocampus is particularly notable for its involvement in neurodegenerative diseases, especially Alzheimer's Disease, where it is one of the first brain regions to show pathological changes and functional decline. [2]
The hippocampus is a pair of seahorse-shaped structures in the medial temporal lobes, critical for: [3]
The hippocampus receives major input from the entorhinal cortex, which itself receives processed information from virtually all associational cortical areas, making the hippocampus a critical hub for integrating diverse sensory and cognitive information. [4]
The hippocampus consists of several distinct subregions, each with unique cellular composition and connectivity: [5]
Dentate Gyrus: Contains the granule cells that give rise to mossy fiber axons. The dentate gyrus is one of two brain regions that maintain adult neurogenesis throughout life. The hilus (polymorphic layer) lies between the granule cell layer and CA3.
CA3 (Cornu Ammonis 3): Receives input from dentate gyrus granule cells via mossy fibers. CA3 pyramidal neurons have extensive recurrent collateral connections with other CA3 neurons, forming an auto-associative network critical for memory storage and pattern completion. CA3 also projects to CA1 via Schaffer collateral axons.
CA2: A small region between CA3 and CA1 that shows resistance to excitotoxicity and certain neurodegenerative processes. CA2 pyramidal cells project to the lateral septum and receive input from hypothalamic oxytocin-producing neurons.
CA1 (Cornu Ammonis 1): The primary output region of the hippocampus, receiving input from CA3 via Schaffer collaterals and directly from the entorhinal cortex via the perforant path. CA1 pyramidal neurons are exquisitely vulnerable to ischemia, excitotoxicity, and tau pathology in Alzheimer's Disease.
Subiculum: The major output structure of the hippocampus, projecting to the entorhinal cortex, hypothalamus, amygdala, and septal nuclei.
The hippocampal formation includes: [6]
The hippocampus contains multiple neuron types: [7]
The hippocampus is essential for multiple forms of memory: [8]
The hippocampus generates characteristic oscillations critical for information processing: [9]
The CA1 region exhibits particular vulnerability to various insults:
The classic hippocampal circuit proceeds:
This trisynaptic circuit provides a sequential processing pathway for cortical information.
The hippocampus is one of the earliest and most severely affected regions in AD:
The hippocampus is also affected in Parkinson's Disease, particularly in patients with mild cognitive impairment (MCI) or dementia:
The hippocampus is implicated in numerous other conditions:
Squire LR, et al. Memory consolidation, replay, and systems consolidation: A functional framework. Neuron. 2020;107(1):4-16. Memory consolidation, replay, and systems consolidation: A functional framework. 2020. ↩︎
Kempermann G, et al. Human adult neurogenesis: Evidence and remaining questions. Cell Stem Cell. 2018;23(1):25-30. Human adult neurogenesis: Evidence and remaining questions. 2018. ↩︎
Rolls ET, Kesner RP. A computational theory of hippocampal function, and tests of the theory. Prog Neurobiol. 2006;79(1):1-48. A computational theory of hippocampal function. 2006. ↩︎
Palop JJ, Mucke L. Amyloid-beta-induced neuronal dysfunction in Alzheimer's disease: From synapses toward neural networks. Nat Neurosci. 2010;13(7):812-818. Amyloid-beta-induced neuronal dysfunction in Alzheimer's disease. 2010. ↩︎
Eichenbaum H. Hippocampus: cognitive processes and neural representations that underlie declarative memory. Neuron. 2004;44(1):109-120. Hippocampus: cognitive processes and neural representations. 2004. ↩︎
Jack CR Jr, et al. Hypothetical model of dynamic biomarkers of the Alzheimer's pathological cascade. Lancet Neurol. 2010;9(1):119-128. Hypothetical model of dynamic biomarkers of the Alzheimer's pathological cascade. 2010. ↩︎
Goldman JG, et al. Hippocampal volume loss in Parkinson's disease with mild cognitive impairment. Mov Disord. 2020;35(3):488-495. Hippocampal volume loss in Parkinson's disease with mild cognitive impairment. 2020. ↩︎
Sorrells SF, et al. Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults. Nature. 2018;555(7696):377-381. Human hippocampal neurogenesis drops sharply in children. 2018. ↩︎
Garbarino IR, et al. Neural circuits for navigation. eLife. 2019;8:e49298. Neural circuits for navigation. 2019. ↩︎