cortico-hippocampus circuits and cell types that process memory

information-processing model of memory

proposes that there are three stages of memory processing: encoding, storage, and retrieval

encoding

the first stage of the information-processing model of memory that involves perceiving some stimulus event and translating/encoding that information so it can be easily stored in our brains

during encoding

info is associated with what we have already experienced and know; we categorize and organize this information in a meaningful way for storage and future recall

storage

process through which encoded material becomes retained over time in our memories; biological changes occur in the brain to allow these memories to be stored

retrieval

the last stage of the information-processing model of memory; generally, the more effort we put into preparing information for storage, the easier we can retrieve it later

memories during retrieval

are vulnerable to change

the neural cartographer

nickname for Wilder Penfield, who attempted to treat patients with epilepsy. He stimulated the brain with electric current to find the location of seizures, and his surgeries were often successful

when stimulating the temporal lobe

some patients reported vivid recall of memories and sometimes even hallucinations after temporal lobe stimulation

animal models allow

specific brain lesions or activation to test causality, test experimental drugs, record activity of individual cells

Institutional animal care and use committee (IACUC)

a team of qualified experts, vets, and members of the community must evaluate the design, methods, and potential outcomes of an experiment with animals to promote the highest care for animals in research

interpret results from animals with care

Animal models cannot capture the full complexity of mental illnesses as seen in humans; care must be taken when generalizing from one organism to another

words matter

NIMH recommends using the models “for” addressing neurobiological questions rather than models “of” specific mental health conditions. NIMH also strongly discourages the description of animal behaviors in terms of emotions and thought processes that are only accessible to humans by self-report or clinical diagnoses

the medial temporal lobe (MTL) contains

entorhinal cortex, hippocampus, parahippocampal cortex, perirhinal cortex, amygdala

hippocampal formation includes

entorhinal cortex, dentate gyrus, hippocampus (Cornu Ammonis 3, 2, 1), subiculum, parahippocampal cortex

hippocampal complex (HPC)

sensory modalities begin to converge in adjacent hippocampus areas and finally come together to make a rich representation possible in the

cortico-hippocampus system

system thought to process spatial and temporal information

hippocampal formation function

helps us encode, store, and retrieve memories

pyramidal neurons

largest neurons in the brain found in the hippocampus, cerebral cortex, and amygdala, always excitatory and releases glutamate, has complex dendritic branching; projection neurons that send signals to distant places

granule cells

very small cell bodies found in the hippocampus and other parts of the cortex and cerebellum, has cone-shaped dendritic trees, may be excitatory or inhibitory and primarily releases glutamate but something GABA; capable of neurogenesis

inhibitory interneurons

makes up 10-15% of the total cell population in the hippocampus, always inhibitory and releases GABA, and mostly coordinates local activity

trisynaptic circuit pathways

perforant, mossy fiber, schaffer collateral pathways

perforant pathway

pyramidal cells in the entorhinal cortex project to granule cells in the dentate gyrus

Mossy Fiber Pathway

cells in the dentate gyrus project to pyramidal cells in CA3

Schaffer Collateral Pathway

Cells in CA3 project to pyramidal cells in CA1, CA1 neurons then project to the subiculum

subiculum

the major output of the hippocampus

Morris Water Maze

healthy rats were able to find a submerged platform and remember its location, but rats with damage to the hippocampus fail to remember the submerged platform’s location

single-cell electrophysiology

placing an electrode near the neuron’s cell body and recording the signal to measure how neurons communicate

recording electrode

eavesdropping on the brain in or near the neuron soma

reference electrode

measuring the difference in electrical voltage some distance away so it is not affected by electrical signals

in vivo electrophysiology

listening in on the brain in real time; when a neuron fires, it leaves a detectable electrical current that can be picked up by electrodes and analyzed using specialized software

place cells

cells that fire in specific locations in space as an animal explores an environment; are thought to represent a map of the space around us; located in the hippocampus

place field

certain nerve cells were active when a rat reaches a particular place in the environment, the environment is known as

internal neural map

different place cells become active at different places and the combination of activity in many pace cells creates a neural map that represents a particular environment

global remapping

place cell changes its location of firing in a new environment

rate remapping

place cell changes the amount it fires in the same environment

grid cells

a single cell fires or gets activated when a rat reaches a particular location in an environment. These locations are arranged in a hexagonal pattern

splitter cells

cells in the hippocampus that fire depending on an animal’s goal and represents spatial episodes/routes; some will fire when the goal is to go left and others when the goal is to go right, can fire at the same location on the stem of the maze but only if the animal goes left or right

time cells

cells in the hippocampus that keep track of time; for example when there’s a task where an animal has to wait 10 seconds before making a choice

time fields

the seconds they spend firing

sensory coding types

specificity, sparse, and population

specificity coding

1 specialized neuron responds to 1 stimulus; the jennifer aniston neuron

sparse coding

a stimulus is represented by the pattern of firing in a small group of neurons

population coding

our experiences can be represented by the pattern of firing across a large number of neurons

social transmission of food preference

healthy rats show a preference for demonstrator odor foods, rats with hippocampal lesions fail to show a preference

memory space

the hippocampus is important for creating a memory space as opposed to only processing spatial memory

cognitive maps

connect disparate pieces of information into meaningful associations and sequences