Hippocampus, Memory, and Neuroplasticity

Vocabulary practice flashcards covering hippocampal anatomy, memory processing, long-term potentiation, cholinergic signaling pathways, and microtubule function based on lecture slides by Prof. Mark Yeoman.

Patient H. M.

A patient who underwent bilateral surgical resection of the hippocampus in 1953 to manage intractable epilepsy; his inability to form new memories after the surgery established the essential role of the hippocampus in memory formation and cognition in 1957.

Episodic memory

A subcategory of explicit (conscious) long-term memory that encompasses memories of specific personal events and experiences that happened to an individual; characteristically lost first in Alzheimer's disease alongside short-term memory.

Semantic memory

A division of explicit (conscious) long-term memory dedicated to the acquisition and storage of general conceptual knowledge and factual information about the world.

Procedural memory

A division of implicit (unconscious) long-term memory responsible for motor skills, habit learning, and physical actions, such as riding a bicycle.

Hippocampus

A curved limbic structure—named after its seahorse-like anatomical shape—that is essential for learning, spatial navigation, and the conversion of short-term memories into long-term memories.

Encoding (memory)

The initial phase of memory formation where cortical sensory inputs (e.g., visual, auditory) are processed and directed to the hippocampus, where they are initially stored and linked together to generate a unique memory trace.

Cellular consolidation

A short-term stabilization process wherein a memory trace is reinforced in the hippocampus through cellular and structural alterations, primarily mediated by long-term potentiation ($\text{LTP}$).

System consolidation

The gradual neurobiological process by which stabilized memories are transferred from temporary hippocampal storage to the neocortex for enduring, long-term storage.

Perforant path

The primary input pathway to the hippocampus originating in the superficial layers of the entorhinal cortex ($\text{EC}$) and terminating on granule cells of the dentate gyrus ($\text{DG}$) at Synapse 1.

Mossy fiber pathway

The hippocampal axonal tract formed by dentate gyrus ($\text{DG}$) granule cells projecting to pyramidal neurons in the $\text{CA3}$ subfield at Synapse 2, characterized by non-associative long-term potentiation ($\text{LTP}$).

Schaffer collateral pathway

The hippocampal axonal projection originating from $\text{CA3}$ pyramidal neurons and terminating on $\text{CA1}$ pyramidal neurons at Synapse 3, exhibiting associative long-term potentiation ($\text{LTP}$).

Long-term potentiation (LTP)

A sustained increase in synaptic transmission efficiency following high-frequency electrical stimulation (tetanus), observable electrophysiologically by an elevated slope of the excitatory postsynaptic potential ($\text{EPSP}$) and insertion of additional $\text{AMPA}$ receptors.

Basal forebrain cholinergic nuclei

Three subcortical clusters containing acetylcholine-producing neurons: the medial septal nuclei, the nucleus basalis of Meynert, and the diagonal band of Broca.

Medial septal nuclei

A cholinergic nucleus in the basal forebrain that directly projects to and innervates the hippocampus to modulate memory formation.

Nicotinic acetylcholine receptors (nAChRs)

Fast-acting, ligand-gated ion channels (ionotropic) responsive to nicotine and acetylcholine that conduct cations such as $\text{Na}^+$ and $\text{Ca}^{2+}$, found in skeletal muscle ($\text{N}_\text{M}$), autonomic ganglia ($\text{N}_\text{G}$), and the central nervous system.

Muscarinic acetylcholine receptors (mAChRs)

Metabotropic G-protein coupled receptors ($\text{M}_1\text{--}\text{M}_5$) responsive to muscarine that transduce signals via $\text{G}_q$ or $\text{G}_i$ proteins across glands, cardiac tissue, vascular endothelium, smooth muscle, and the central nervous system.

Alpha7 nicotinic receptor ($\alpha 7\text{ nAChR}$)

A homopentameric ionotropic receptor constructed from five $\alpha 7$ subunits with substantial $\text{Ca}^{2+}$ permeability, which triggers downstream intracellular signaling cascades ($\text{MEK/ERK}$, $\text{CaMK/PI3K/Akt}$, and $\text{JAK2/STAT3}$) critical for neuroprotection and plasticity.

Cholinergic modulation of memory encoding

The physiological effect of acetylcholine wherein it tones down the neocortical memory consolidation pathway to facilitate optimal and efficient temporary memory encoding within the hippocampus.

Microtubules

Cylindrical polymeric protein structures composed of tubulin heterodimers organized around a central lumen, possessing distinct plus and minus ends, essential for neuronal morphology, neurite outgrowth, and intracellular trafficking.

Tau protein

A microtubule-associated protein that normally bears $2\text{--}3\,\text{moles}$ of phosphate per mole of tau at low basal levels, functioning to stabilize polymeric microtubules to permit neurite extension and structural maintenance.

Kinesin

An ATP-dependent motor protein that carries cargo, such as synaptic vesicles, anterogradely from the neuronal soma toward the distal axon terminals along microtubules.

Dynein

An ATP-dependent motor protein that drives retrograde axonal transport along microtubules, conveying organelles and endocytic vesicles from peripheral terminals back to the neuronal cell body.