Understanding Receptive Fields

Brain Cells

• Neurons, numbering 86 billion, act as the brain's messengers, signaling changes related to the environment, internal states, and action plans.
• Glia support neurons by regulating the chemical content of extracellular space.
• Glia insulates axons and consists of astrocytes, oligodendrocytes, and Schwann cells, outnumbering neurons.
• Other brain cells include ependymal cells, which line fluid-filled ventricles and guide cell migration.
• Microglia removes debris and vasculature in the brain consists of blood vessels.

Neuron Anatomy

• The neuron is composed of a cell membrane, dendrites, an axon, an axon hillock, an axon terminal, and a cell body (soma).
• The cell membrane is a lipid bilayer containing proteins that controls what comes in and out.
• Dendrites receive input from other neurons at synapses, acting as antennae.
• The axon provides input to other neurons and is the highway where signals travel.
• The axon hillock is the site of action potential generation.
• The axon terminal that forms part of the synapses is the mailbox that sends messages to the next neuron.
• The soma functions as a gene expression and transcription center, facilitates protein sorting, and generates cellular respiration energy.
• The soma is responsible for protein synthesis and transcription and also contains cytosol.

Electrical Theory Basics

• Protons possess a positive charge and electrons possess a negative charge.
• An atom has a positive charge when it has fewer electrons.
• A negative charge indicates there are more electrons.
• Important ions are sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl–).
• An electric field is created by positive and negative charges.
• Positive ions are drawn to negative charges, while negative ions are drawn to positive charges.
• Electric potential is the energy required to move a positive ion.
• Positive ions possess more energy when they are near a positive charge and lose energy as they move towards negative charges.
• Potential difference is the difference in electric potential between two points, measured in volts (V), but usually millivolts (mV) in neurons.
• Current is the movement of charged particles, like sodium (Na+) and potassium (K+), from one point to another.
• The cell membrane is not permeable to ions and separates them.
• A concentration gradient refers to the varying levels of ions inside versus outside the neuron.
• Ions flow from areas of high concentration to areas of low concentration.
• Potassium (K+) concentration is high inside the cell and sodium (Na+) is high outside the cell.
• Ion channels selectively allow ions to pass through the membrane's inside and outside.

Membrane Potential

• Changes in membrane potential encode information
• At the resting membrane potential, potassium ion concentration is higher inside the cell, while sodium ion concentration is higher outside the cell.
• Membrane potential indicates the electrical potential difference between the cell's inside and outside.
• When ion channels open, positive ions move toward a more negative compartment.
• Resting membrane potential: The cell's inside is more negative than its outside due to negatively charged proteins, representing a negative vibe.
• Depolarization occurs when the cell gets excited, causing membrane potential to become less negative or more positive.
• Hyperpolarization is the opposite of depolarization, causing the membrane potential to become more negative.

Ion Movement & Equilibrium Potential

• Ions diffuse evenly across the membrane if there are no other driving forces.
• Ion movement depends on the concentration gradient and electric potential difference.
• Equilibrium potential is the electrical potential that balances ionic concentration gradients.
• Potassium (K+) is key for resting potential because neurons are permeable to it at rest.
• Potassium channels at rest cause leak currents that create a negative charge inside the cell.

Voltage Gated Ion Channels

• These channels, or doors, open based on the membrane's electrical charge, and sodium (Na+) and potassium (K+) are only permitted when the conditions are favorable.
• Charged protein subunits of a channel change conformation based on membrane potential.
• Ligand-gated ion channels open using a transmitter/messenger (ligand).
• The binding of a ligand alters the channel's conformation, and examples include the AMPA positive ion channel and the GABA chloride channel.
• In depolarization, sodium (Na+) channels open as the membrane depolarizes, becoming more positive, which causes sodium influx.
• Channels stay open briefly and cannot be immediately reopened due to inactivation.
• Threshold: The critical membrane potential value at which sodium (Na+) channels open, generating an action potential, with a membrane potential around -45mV.

Action Potential Propagation

• The primary driving force for the rising phase of action potentials is sodium ions flowing in through sodium channels.
• Efflux of positively charged potassium ions makes the outside of the cell more positive, helping the membrane potential return to resting potential and contributing to the falling phase.
• Action potential travels by brief changes in membrane potential and is an all or nothing event.
• Action potential travels from −70mV to +30mV and back, carrying information over long distances along the axon and to connected cells.
• After the absolute refractory period, a cell can generate more spikes if it depolarizes to the threshold.
• Depolarizing phase: sodium moves in, sodium channels open, inward sodium current
• Hyperpolarizing phase: potassium moves out, sodium channels close, more potassium channels open, outward potassium current (resets potential)
• To continue generating action potentials, we need to re-establish concentration gradients by moving sodium back out of the cell and more potassium back in
• The sodium-potassium pump maintains the concentration gradients by transporting Na+ and K+ back across the membrane against their concentration gradient, consuming energy.

Action Potential Path

• It begins at the axon hillock, generates along the axon with a chain reaction mechanism, and reaches the axon terminal.
• It travels from the axon hillock to the axon terminal, and sodium influx depolarizes the membrane ahead to threshold.
• Chain reaction: action potential generates and regenerates along axon
• Action potential spreads along the membrane with conduction velocity.
• It can also travel toward the cell body, causing back propagation.

Cell membrane

• It separates ions into sodium outside and potassium inside.
• Potential differences occur across it, and its resting potential has an inside that is more negative than outside.
• Action potential is generated when the cell depolarizes to the threshold as sodium channels open and cause a Na+ influx.
• Membrane potential repolarizes when potassium channels open and cause a K+ efflux.
• It transmits action potential along axon to the next cell across the synapse.

Single-Neuron Recordings

• Intracellular recordings measure action potentials and subthreshold fluctuations of the targeted cell.
• Extracellular recordings record action potentials from nearby cells, sorting spikes based on shape and summing subthreshold fluctuations into local field potentials (LFP).
• Intracellular recordings reveal both subthreshold dynamics and action potentials, while extracellular mainly record spikes and summed fluctuations for local field potentials.
• Classical (few microns of metal exposed at tip), matrix, laminar probes (multiple electrode contacts), utah array.
• Neuropixels offer high-density, high-precision measurements.
• Small exposed tips have high resistance, sample smaller areas, and are best for isolating individual neurons.

Impedance

• It measures resistance plus electrode capacitance.
• Higher impedance allows smaller, fine-tipped electrodes to isolate spikes from individual neurons.
• It allows larger tips (e.g., ECoG) unable to isolate single cells.
• Greater distance results in smaller spike amplitude

Local Field Potentials (LFP)

• LFP involves fluctuations summed up by neurons nearby
• It is a measurement of combined electrical activity of a large group of neurons in a small brain area.
• LFP from depth electrodes reflects up to 1,000 cells, mainly within 250 microns.
• ECOG: Electrodes on the brain surface capture superficial cortical layers used in epilepsy research

Electroencephalography (EEG)

• EEG represents activity of the head cap
• It records synchronized neuron activity from the scalp
• It is non-invasive, has low spatial resolution, and poor access to deep brain structure
• Reflects hundreds of thousands to millions of cells
• It is a Summation of synchronized activity of neurons with spatial orientation
• It has difficulties localizing activity because the skull smears the activity making identifying specific locations of activity hard

Functional Magnetic Resonance Imaging (fMRI)

• fMRI measures blood oxygen level signals, reflecting subthreshold activity and better spatial but worse temporal resolution.
• It excites hydrogen atoms with magnetic fields.
• Its blood oxygenation changes reflect neural changes
• Brain divided into cubes used in fMRI studies: changes in signal size around 2%, commonly 100,000 voxels are used

Brain recording methods

• Single-unit methods may be invasive, reflects one cell, has high spatial resolution, good temporal resolution
• LFP methods may be invasive, reflects approx. 1000 cells, high spatial resolution, good temporal resolution
• EEG methods are non invasive, reflects approx. One million cells of pour spatial resolution, with good temporal resolution
• FMRI methods are non invasive, reflects approx. Half a million cells of better than EEG resolution, with pour temporal capabilities.

Spike Rate Code

• The brain encodes by the number of neuron spikes over a period of time.
• In spike rate, a stimulus increases intensity that causes neurons to fire more spikes to increase the intensity of a stimulus.

Pooled Response Code

• Coding method looks at total neuron spikes during period of time
• Integrates acts from multiple at once instead of one neuron
• By responses from several net gets clearer more reliable signals due it reduces "noise"

Spike Timing Codes

• Spike codes emphasis WHEN neurons fire the spike
• Brain pays attention to spike timing relative to each other
• Includes Spike-Phase Code. and Spike Pattern Code

Labeled-Line Code

• Brain encodes info on WHICH neurons are firing and # of spikes in production
• "label" for each neuron in the system. Decoding neural activity: Pattern Classifier
• Is algorithm for date from multiple neurons and predict category or class
• 2 Decoding process: training step THEN test step
• First get subsystem data from neural data and classifier learns how neural patterns Then classier learns how neural patterns from the categories

Neural Data

• Receives now neural from training
• Predicts how categories belong-based on patterns learners
• Can predict based on “gray dot” visual

How it works

Imagine have several neurons and images

In training step

Different images correspond to different spikerates presented by red or blue dots.

• In the tester classifier will assign new spike data related by grey dot to the closest category from training day

FMRI

• In Fmr1 functional magnetic response it has too measure brain activity but has more noise then other methods.
• Decoding fmri data from singlebrain can lead into inaccurate result due to noise.
• Requires and invasive technique ,record of all spikes
• FMR1 ISNT Noninvasive but unportable

Requirement:

Stabilizerterm recordings to produce immediate feedback or control actings Brain plsaticity means brain need adapt adapt feedback from devies

Neural codes fall into main cathehory

• Spike rate
• spike timing code
• much evidence support in coding in brain,decoding on its basis stimulus,genrel agreement on importanatnence

1. Brain Anatomy Overview

• Lobes:Brain divided into different lobes (frontal, temporal, parietal, occipital),each responsible for specific function like motor control,sensory perception,and vision.
• Frontal= motor control, decision making and planning.
• Temporal, hearing
• Parietal= touch , spatial transformation

2. Navigating the Brain (Anatomical Terms):

• Anterior/Rostral (front)
• Posterior/Caudal (back)
• Dorsal (top)
• Ventral (bottom)
• Lateral (side)
• Medial (middle)

Thalamic areas

• Pathway cortex and after processing movement to secondary order interpretation areas
• First thalamic areas that major data movement from senosry eye ear skin

Hierarchical Organization of the Cerebral Cortex:

Cerebral cortex is organized in layers/regen to process info

• Primary Sensory ,area that receicves sensory informtioon processes like touch sight and sound
• Secondary Sensory Areas areas take basic sensory data from and mroe complex detainls
• Higher-Order Areashigher order areas processing make abstar and concepts ore anterior

feed forward path ways

Means inromation flows from back (posterior) to the front of the brain _EX Vision sensory info Like the orieantion and the brain more complex details Feedback pathways: -Inforamtion flows front to back of brain ways.

• Feedback can adjuct processsing of things

Pathway of Sensory

Data starts at sensory areas of organ for example eye ear Skin

first higher order

Order thalamus and reciesves eyea send the primary cortex.

• visual info form the eye and recisves to them

primary cortex.

• visual cortex and process simple of the sesnroy eye ears
• After recing from them data starts regien more complex from seorsy to data

direct pathway:

• sensor indirect can travel between to complex region for thebrain alllows processing with regions Sensory data from stimi,fist order processing,primayr cortex,secondary sensory,high order thalamcus/ cortex

DORSAL/ventral path way

dorsal path way guiding acitons with helps yo determine"where" ,ventral in identifing helps you"what" an object

Cerebral Cortex Organization:

• 6layers new vortex with specific regions (6)6layers in the Neocortex Motor/sensory/frontal(4)

Radial Organisation

• radial orgianzation from neuro which go down tend respond simalir neurons respoinds the kind to infro for for specific to featuers

different brain cells

these cells promtoe cell protential the make fire promite Excitatory Cells inhibilatory cells= cell protential reducing acitivity (localized), small and large Excitatory CellsTypes orcell cells-common includes Pyramidal cell -basket cells

10. Canonical Microcircuit of the Cerebral Cortex:

canical is organzed to effience process snesorys help fouc acitivicty filter distraction from contex from a:Layer 4 -sensory data b:2/3 inform ot courtical from areas c:5 inform subcordial for data data d:5-infolm back from cord to area d-f:1 from other areas

Brains Across Specie

more more structural with high order areas complex with in other human brain,smal brain,more complex procesing,and High complex

Brain circuit

involvate the to motor skills of key actions Helps to decise past learning Example :Motor control

• cortex nucleaus

Synaptic Transimssion and Plasticity

definition -A is the connection from 2 nuerons"axon presy contact -Neurotransmitter

• GABA,inhibiroty and Glutamanare from main exciotry

Receptor

protien cells membrance Nuertornasmany -gaited chssnyh

4,synmatic placticty

• refers how efficeve that involved in Axon and

5,synmatic placticty

• impact can signifncntly influnece action to the post synapse commonto cell

synatic claft

small that space between presnay post synapse to cell

Active Zone

• synatic ,nuertoranas A

1. the pre with Neurotransmitters terminal with "action zone."
2. An cell of increase presynaptic calcium Ca2+ 3..The triggers The to trigger

calcium

to the cell.

Receptors

• contian neurton binding domain open The opening ion change in potential either inhibitory post These influence cellular and slower compafre iontropic recotors

Transmutter

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Memory(2.13/2025Memory)

Amnesia new

The Brain

Hippocampus hippocampus,. from

Hippocampus

Separation of Similar

• the , and that "where,.1.

• Action,

• Resting, . that resolve. highsingle,-Ganglia Networkschizopbernia,1+3

• Recepti and and direction-and directionand