Hippocampus
Neuroscience
Brain structure critical for memory, with distinct laminar organization.
The hippocampus is a curved structure deep in the temporal lobe, critical for memory formation and spatial navigation. It has a distinct laminar organization different from cortex, with well-characterized field potentials and cell types.
Anatomical organization:
- CA1: Large pyramidal cell layer, output stage
- CA3: Recurrent network, pattern completion
- Dentate Gyrus: Sparse granule cells, pattern separation
- Subiculum: Transition to cortex
Characteristic signals:
- Theta rhythm (6-12 Hz): Movement and attention-related LFP oscillation
- Sharp-wave ripples (150-250 Hz): Memory consolidation during rest/sleep
- Place cells: Location-selective single-unit activity
- Grid cells: Spatial periodic firing (in medial entorhinal cortex)
Recording considerations: Hippocampal recordings often span 1-2 mm to cover multiple subfields. Theta rhythm serves as a useful functional marker that recording sites are in hippocampus. High site density helps distinguish CA1, CA3, and dentate layers.
Probe depth: In mice, hippocampus is ~2-3 mm deep from brain surface. In rats, ~3-4 mm. Requires probes with sufficient length and rigidity to reach these depths reliably.