Psychology 454 Unit 1

Lecture 1: 1.21.25

Mind Reading in Neuroscience

• Understanding the brain signals necessary for reading minds involves several key questions:

  • What brain cells should be measured?

  • Which signals from these cells are informative?

• Importance of this research:

  • Development of medical treatments.

  • Creation of neural prostheses.

Types of Brain Cells

• Two main types of brain cells:

  • Neurons:

    • Total count: 86 billion neurons in the brain.

    • Function: Signal changes in the environment, internal states, and action plans.

  • Glia:

    • Function: Regulate the chemical environment and insulate axons of neurons.

    • Specific types include:

      • Astrocytes: Regulate extracellular space.

      • Oligodendrocytes and Schwann cells: Insulate neuron axons.

    • Ratio: Approximately 10 times more glia than neurons in thalamus, midbrain, and brainstem; about 1.5 times more glia than neurons in the cerebral cortex.

  • Other Cell Types:

    • Ependymal cells: Line ventricles and guide migration of brain cells during development.

    • Microglia: Clean up debris from damaged neurons and glia.

    • Vasculature: Includes arteries, capillaries, and veins.

Anatomy of a Neuron

• Cell Membrane:

  • Acts as the boundary of the cell.

  • Composed of lipid bilayer with proteins (receptors, channels).

• Dendrites:

  • Receive inputs from other neurons (post-synaptic).

• Axon:

  • Transmits impulses to other neurons.

  • Axon Hillock: Site where action potentials are generated.

  • Axon Terminal: Forms synapses (pre-synaptic).

• Cell Body (Soma):

  • Contains the nucleus for gene expression and transcription.

  • Involved in protein synthesis (Rough ER, Ribosomes), sorting (Smooth ER, Golgi apparatus), and cellular respiration (Mitochondria).

  • Cytosol: The fluid inside the cell.

Basics of Electrical Theory in Neurons

• Electric Charge:

  • Atoms consist of protons (positive), electrons (negative), and neutrons (neutral).

  • An atom's charge depends on the number of protons vs. electrons.

• Important Ions for Neuronal Signals:

  • Positively charged: Sodium (Na+), Potassium (K+), Calcium (Ca2+).

  • Negatively charged: Chloride (Cl–).

Electric Fields and Current

• Electric Field:

  • Created between positive and negative sources; ions move according to their charge in relation to the field.

• Electric Potential:

  • Energy required to move a positive ion in a field; potential difference is the difference in potential energy between two sites, measured in volts.

Ion Concentration Across the Cell Membrane

• Cell Membrane:

  • Separates ions but is not permeable to them.

• Concentration Gradient:

  • Areas of high to low ion concentrations lead to ionic flow.

• Ion Channels:

  • Selectively allow specific ions to pass through, bridging the inside and outside of the cell.

Membrane Potential

• Definition:

  • Difference in electric potential across the cell membrane; reflects charge separation.

• Resting Membrane Potential:

  • Typically around -65 to -70mV when a cell is at rest (inside negative relative to outside).

• Ion Movement:

  • Changes in membrane potential occur due to ion movement when channels open.

• Changes in Potential:

  • Depolarization: Membrane potential becomes less negative (more positive).

  • Hyperpolarization: Membrane potential becomes more negative.

Ion Movement Equilibrium

• Ions will diffuse evenly across a membrane in the absence of driving forces.

• Movement of ions is influenced by concentration gradients and electric potential differences.

• Equilibrium Potential (Eion): The electrical potential that balances a concentration gradient.

• K+ ions are key to determining resting membrane potential due to leak currents through potassium channels.

Classes of Ion Channels

• Voltage-Gated Ion Channels:

  • Open at specific membrane potentials and are critical for action potentials.

• Ligand-Gated Ion Channels:

  • Open in response to neurotransmitter binding, altering ion permeability (e.g., AMPA & GABA receptors).

Membrane Potential Threshold

• Na+ Channel Activation:

  • Opens during depolarization for about 1ms and then inactivates, leading to the absolute refractory period.

• Membrane Potential Threshold:

  • The critical value needed to trigger an action potential, usually around -45mV.

Action Potential Dynamics

• Action Potential:

  • A rapid, all-or-nothing change in membrane potential occurring within 1ms, typically from -70mV to +30mV and back.

  • Transmits information over long distances down the axon.

• Phases of Action Potential:

  • Depolarizing Phase: Na+ channels open, allowing sodium influx.

  • Hyperpolarizing Phase: Na+ channels close while K+ channels open, allowing potassium efflux, resetting potential.

• Ion Gradient Restoration:

  • Sodium-potassium pump transports Na+ out and K+ back into the cell to restore gradients, consuming ATP.

Propagation of Action Potential

• Travels from the axon hillock to the axon terminal (orthodromic conduction).

• The influx of sodium during an action potential depolarizes adjacent membrane areas, generating a chain reaction.

Summary of Key Points

• Ion Separation in Cells:

  • More sodium outside, more potassium inside.

• Electric Potential Difference:

  • Resting membrane potential is negative inside relative to outside.

• Action Potential Mechanism:

  • Generated when the cell is depolarized to threshold, initiated by Na+ channel opening.

• Signal Transmission:

  • Action potentials travel along the axon to synapses for communication with other neurons.

Lecture 2: 1.23.25

Single-Neuron Recordings

• Types of Recordings:

  • Intracellular Recordings:

    • Capture action potentials from targeted cell.

    • Measure subthreshold membrane potential fluctuations.

  • Extracellular Recordings:

    • Capture action potentials (spikes) from nearby cells.

    • Include local field potentials (LFP) derived from summed subthreshold fluctuations from nearby cells.

    • Spikes are sorted based on characteristics like shape to isolate individual cells.

Electrode Types for Extracellular Recordings

• Types of Electrodes:

  • Classical Electrode:

    • Basic design for recording neuronal activity.

  • Matrix Electrode:

    • Features multiple recording sites.

  • Micro-electrode:

    • Small metal tip, high impedances useful for isolating neuron spikes.

  • Neuropixels Probe:

    • Contains multiple recording sites; advanced technology for detailed readings.

  • Utah Array:

    • 3D arrangement of microelectrodes for high spatial resolution recording.

• Electrode Specifications:

  • Tip Size: Smaller tips yield higher resistance and sample smaller brain areas.

  • Impedance: Important for neuron isolation; fine tips can isolate spikes at >1 megaohm impedance.

Local Field Potential (LFP) Recordings

• Characteristics of LFP:

  • Reflects activity from approximately 1,000 cells, within 250 microns of electrode tip.

  • Useful for understanding synchronized neuronal activity over larger areas.

  • Commonly derived from:

    • Extracranial depth electrodes.

    • Electrodes placed on brain surfaces during epilepsy surgeries (ECoG).

Electroencephalography (EEG)

• Features of EEG:

  • Reflects activity from hundreds of thousands of neurons.

  • Summation of synchronized activity, predominantly from pyramidal cells.

  • Non-invasive method, offers poor spatial resolution due to skull interference but good temporal resolution.

Functional Magnetic Resonance Imaging (fMRI)

• How fMRI Works:

  • Excites hydrogen atoms in the brain using magnetic fields.

  • Measures radio frequency emitted signals; indirect measure of neural activity (BOLD).

  • Better spatial resolution than EEG, often 2x2x2mm.

  • Poor temporal resolution, typically samples every 2 seconds.

Comparing Brain Recording Methods

• Table of Methods:

  • Single-Unit: Invasive, reflects 1 cell, <30μm spatial resolution, ≤1ms temporal.

  • LFP: Invasive, ~1,000 cells, ≈250μm spatial resolution, ≤1ms temporal.

  • EEG: Non-invasive, ~1,000,000 cells, >5mm spatial resolution, ≤1ms temporal.

  • fMRI: Non-invasive, ~500,000 cells, ≈2x2x2mm spatial resolution, ≈2s temporal.

Neural Information Coding

• Spike Rate Code:

  • Quantity of spikes over specified time; evidence supports rate coding linked to stimulus intensity.

  • Pooled response from multiple cells reduces variability (noise).

• Other Neural Coding Mechanisms:

  • Spike Timing Codes: Variability in timing may represent additional information beyond sheer numbers.

• Spike Pattern Code: Temporal patterns provide more informative spikes per interval.

• Labeled-Line Code: Specific neuronal firing patterns and their quantities convey complex information.

Decoding Neural Activity

• Process Overview:

  • Pattern Classifier: Multivariate analysis to predict recorded image categories.

  • Training Step: A subset of neural data is used to train classifiers.

  • Test Step: New data is categorized based on closest predictions.

Neural Prostheses

• Signal Measurement Choices:

  • Spikes (invasive), LFP (invasive), fMRI (non-invasive but not portable), and EEG (non-invasive and portable).

  • Requirements: Long-term stable recordings from many neurons and real-time data analysis.

• Current Developments:

  • Development of EEG-based neural devices and intracranial implants.

Summary of Findings

• Neural Codes: Two categories: spike rate codes and spike timing codes.

  • Significant evidence for the importance of spike rate coding in neural activity.

  • Evidence also exists that spike timing can enhance decoding accuracy in neural communications.

• Implications for Research: Understanding these mechanisms aids in developing neural prostheses and predicting brain behavior.

Lecture 3: 1.28.25

Navigating the Brain

• Layperson terminology:

  • Front, Back, Top, Bottom, Side, Middle

• Neuroscientist terminology:

  • Anterior or Rostral

  • Posterior or Caudal

  • Dorsal

  • Ventral

  • Lateral

  • Medial

• Translation acronym: D V A P L M

Gross Brain Anatomy and Function

• Brain Lobes & Functions:

  • Frontal Lobe: Decision-making, planning, motor control

    • Features:

      • Sulcus (fissure)

      • Gyrus (ridge)

      • Central sulcus

  • Parietal Lobe: Touch, spatial transformations

  • Temporal Lobe: Hearing, higher-level vision

  • Occipital Lobe: Vision

Broad Divisions of the Brain

• Key Structures:

  • Precentral gyrus (motor cortex)

  • Striatum

  • Hypothalamus

  • Frontal Lobe

  • Olfactory receptors

  • Pituitary gland

  • Midbrain

  • Pons

  • Medulla

  • Brainstem

  • Central sulcus

  • Postcentral gyrus (somatosensory cortex)

  • Parietal Lobe

  • Corpus callosum

  • Cingulate cortex

  • Spinal cord

  • Thalamus

  • Occipital Lobe

  • Cerebellum

Pathways for Sensory Information to Primary Sensory Cortex

• Primary Sensory Areas:

  • Primary auditory cortex (A1)

  • Primary visual cortex (V1)

  • Primary somatosensory cortex (S1)

• Thalamus Role:

  • Receives sensory input (eye, ear, skin)

  • Major input areas referred to as "first-order thalamic areas"

Beyond Primary Sensory Cortex: Higher-Order Cortical Areas

• Regions:

  • Prefrontal association area (personality)

  • Primary motor area

  • Premotor area

  • Primary somatosensory area

  • Secondary sensory areas (visual, auditory)

  • Wernicke's area (language comprehension)

Feedforward and Feedback Pathways

• Brain Hierarchical Organization:

  • Primary sensory areas (low-level info) to higher-order areas (complex info)

• Feedforward Pathways:

  • Direction: Posterior to anterior

  • Carry sensory information about the environment

  • Higher-order information processed anteriorly

• Feedback Pathways:

  • Direction: Anterior to posterior

  • Carry information on goals, priorities, predictions

  • Modulate activity in posterior areas to amplify or filter info based on context

Pathways from Primary Sensory Cortex to Higher-Order Cortex

• Structure of Pathways:

  • Includes connections:

    • Primary sensory cortex

    • Secondary sensory cortex

    • Higher-order sensory cortex

    • Higher-order thalamus

    • Feedforward and feedback routes

Parallel Pathways Across the Cerebral Cortex

• Pathways:

  • How (Where) Pathway: Dorsal cortex enabling sensory-guided actions

  • What Pathway: Ventral cortex enabling object perception

Structural Differences Across the Cerebral Cortex

• Neocortex Layers:

  • Contains six layers, differing by brain area

• Cytoarchitectonics:

  • Arrangement of neurons in the brain

• Cytoarchitectonic Maps:

  • Example: Brodmann (1909)

Columns: Fundamental Computational Units of the Cortex

• Vertical Organization:

  • Neurons share similar response properties in a radial fashion.

  • Types:

    • Cortical column: Extends through cortical layers (0.4-0.5 mm in diameter)

    • Cortical minicolumn: Sub-column structure (about 30-50 microns)

Cell Types in the Cerebral Cortex

• Types of Cells:

  • A: Pyramidal

  • B: Stellate

  • C: Bi-tufted

  • D: Double bouquet

  • E: Small basket

  • F: Large basket

  • G: Chandelier

• Excitatory and Inhibitory Cells:

  • Predominant excitatory cells in certain areas.

Canonical Microcircuit of the Cerebral Cortex

• Connections:

  • Excitatory connections between layers and subcortical areas.

  • Inhibitory connections as part of the microcircuit.

• Functionality:

  • Layer-specific inputs and outputs across cortical areas.

Differences in Brains Across Species

• Examples:

  • Mouse, Macaque, Human

• Significance: Reflect unique adaptations in higher-order areas.

Prefrontal Cortex Granularity

• Granular vs. Agranular:

  • Granular cortex has a developed layer 4; absent in rodents.

• Species Comparison: Differences in density of cortical layers.

Anatomical Structure Provides Insight Into Function

• Cell Level:

  • Considerations on excitatory vs. inhibitory cells and dendritic structures.

• Circuit Level:

  • Analysis of lamination patterns and connection types.

• Systems Level:

  • Understanding interconnectivity of brain areas and functionality.

Summary

• Stages of Information Processing:

  • From peripheral sensory organs to thalamic areas to primary cortical regions.

  • Further processed in higher-order areas with both direct and indirect pathways.

• Cortex Organization:

  • Six horizontal layers and vertical columns; critical for information processing.

• Canonical Microcircuit Functions:

  • Specific connections and outputs related to input processing across layers.

Lecture 4: 1.30.25

Broad Divisions of the Brain

• Precentral Gyrus: Also known as the motor cortex, responsible for planning and executing movement.

• Central Sulcus: Separates the precentral gyrus (motor cortex) and postcentral gyrus (somatosensory cortex).

• Postcentral Gyrus: Also known as the somatosensory cortex, responsible for processing sensory information.

• Frontal Lobe: Involved in reasoning, motor control, and emotions.

• Parietal Lobe: Processes sensory information, including touch, temperature, and pain.

• Occipital Lobe: Responsible for visual processing.

• Temporal Lobe: Involved in auditory processing and memory.

• Cerebellum: Coordinates movement and balance.

• Brainstem: Contains midbrain, pons, and medulla, controlling vital functions.

• Hypothalamus: Regulates homeostasis and the autonomic nervous system.

• Pituitary Gland: Master endocrine gland that controls hormone release.

• Thalamus: Relay station for sensory and motor signals.

• Corps Callosum: Connects the left and right hemispheres.

• Cingulate Cortex: Involved in emotional regulation and processing.

• Striatum: Includes the putamen and caudate nucleus, part of the basal ganglia.

• Spinal Cord: Pathway for messages between the brain and body.

Basal Ganglia Areas

• Basal Ganglia: Composed of striatum (putamen and caudate nucleus) that is crucial for control of movement.

• Components:

  • Cortex: Sends outputs to subcortical structures.

  • Caudate Nucleus: Involved in motor control and learning.

  • Putamen: Works with the caudate for voluntary movement.

  • Thalamus: Relay for sensory and motor information.

  • Subthalamic Nucleus: Plays a role in motor control.

  • Substantia Nigra: Regulates movement precision and reward-based behavior.

  • Globus Pallidus: Part of the regulation of voluntary movement.

  • Hypothalamus: Connects the autonomic nervous system with endocrine functions.

Cortico-Striatal-Thalamic Loops

• Function: Involved in action selection and reinforcement learning.

• Importance of Striatum: Critical for decision-making regarding motor actions.

• Connection to Cortical Areas: Primary visual and auditory cortices are engaged in these loops.

Regulation of Information Processing in the Cortex

• Impact of Basal Ganglia: Influences cortical information processing by regulating the striatum's activity.

• Mechanism:

  • Increased striatal activity can disinhibit the thalamus through the direct pathway.

  • The striatum inhibits the globus pallidus internal segment, which allows thalamus activation.

Cortico-Cerebellar System

• Role of the Cerebellum: Engaged in automatic execution of motor skills post-learning.

• Functionality: Integrates both motor and cognitive functions, receives efferent copies from the cortical areas to predict sensory outcomes of movements.

Cortico-Hippocampal Circuits

• Hippocampus Functions: Essential for episodic memory and spatial navigation.

• Involvement of Higher-Order Thalamus: Connects the neocortex and the hippocampus enhancing memory processing.

Six Degrees of Separation

• Concept: Suggests everyone can be connected through six or fewer network connections.

• Milgram's Small World Experiment:

  • Participants were asked to deliver a letter to a distant target using acquaintances.

  • Demonstrated small-world phenomena in social networks.

Network Types

• Regular Network: Each node linked to nearest neighbors.

• Random Network: Nodes randomly interconnected to increase disorder.

• Small-World Network: Combines high clustering with short path length between nodes.

Network Features and Measures

• Node Degree: Represents the number of direct connections a node has.

• Clustering Coefficient: Measures how connected a node's neighbors are relative to the maximum possible connections.

Rich-Club Architecture

• Rich Node: High-degree node with multiple connections.

• Rich Club: A subgraph formed by rich nodes that are interconnected.

Brain Connectivity**

• Anatomical Connections: Connections formed by axon projections.

• Measurement Methods:

  • Tracer Studies: Injecting tracer molecules to track connections.

  • Diffusion MRI: Measures water diffusion to infer connectivity.

• Functional Connections: Correlations in neural activity across different brain areas.

Mapping Anatomical Connections**

• Diffusion MRI Techniques: Identify and visualize brain connections based on water diffusion.

Hubs Based on Anatomical Connections**

• Common Brain Hubs Identified:

  • Precuneus, posterior cingulate cortex, and others noted for significant connectivity.

Mapping Functional Connections**

• Functional MRI: Evaluates correlation of BOLD activity across regions, identifying interactions.

Hubs Based on Functional Connections**

• Consistently Identified Hubs: Match anatomical hubs, like precuneus and cingulate, demonstrating coherence in connectivity research.

Perturbed Brain Networks in Schizophrenia**

• Findings in Disturbances: High clustering and low clustering in patient comparisons.

• Symptoms: Hallucinations, delusions, and cognitive dysfunction linked to network abnormalities.

Summary**

• Cortex and Subcortical Interaction: Key to understanding action and cognition.

• Changes in Brain Networks: Influence disorders and cognitive functions.

• Brain Hub Locations: Critical for understanding overall network functionality.

Lecture 5: 2.4.25

Big Receptive Field Sensors

• Overview: A sensor with a large receptive field can detect anything in a room but lacks specificity in identifying where the object is located.

  • Example Locations:

    • Door 1

    • Door 2

    • Lectern

    • Table

    • Seats

Small Receptive Field Sensors

• Overview: A sensor with a small receptive field detects only the specific seat someone occupies, unable to register others in the room.

  • Example Locations:

    • Door 1

    • Door 2

    • Lectern

    • Table

    • Seats

Intermediate Receptive Field Sensors

• Overview: Useful for detecting people entering or exiting, but cannot identify those already in the hall or in non-front row seats.

  • Example Locations:

    • Door 1

    • Door 2

    • Lectern

    • Table

    • Seats

Importance of Receptive Field Size

• Overview: The size of receptive fields is crucial in accurately identifying people, objects, and places.

Small Receptive Field for Seat Design

• Overview: A relatively small receptive field can distinguish between different seat designs.

  • Example Locations:

    • Door 1

    • Door 2

    • Lectern

    • Table

    • Seats

Identification of Specific Seats

• Overview: Identifies specific seats but cannot differentiate between different environments (e.g., lecture hall vs. Camp Randall).

  • Example Locations:

    • Door 1

    • Door 2

    • Lectern

    • Table

    • Seats

Large Receptive Field for Environmental Differentiation

• Overview: A large receptive field can differentiate between major environments like a lecture hall and Camp Randall.

  • Example Locations:

    • Door 1

    • Door 2

    • Lectern

    • Table

    • Seats

Position Invariance in Sensors

• Overview: Sensors with large receptive fields can identify an object regardless of its position, termed "position invariance."

Optimal Sensor Design Considerations

• Challenges:

  • How to effectively operate across multiple spatial scales?

  • How to localize small objects or parts while identifying larger ones?

  • Achieving position invariance in object identification.

• Environmental Representation:

  • Built from different sizes of receptive fields.

  • Small fields for individual details, larger ones for broader object recognition.

• Creation of Larger Receptive Fields:

  • Achieved by summing inputs from adjacent small receptive fields.

Receptive Fields in Neurons

• Somatosensory Receptive Fields:

  • Smallest in fingertips, largest in thigh/calf.

• Visual Receptive Fields:

  • Smallest: a few minutes of arc; largest: tens of degrees.

Dimensions of Receptive Fields

• Visual Receptive Fields: Mapped in two dimensions of space.

• Somatosensory Receptive Fields: Mapped along body surface dimensions.

• Olfactory Receptive Fields: Governed by carbon chain length of odorants.

• Numerical Receptive Fields: Mapped in terms of numerosity.

Detailed Feature Detection with Small Fields

• Overview: Small receptive fields detect detailed features, but provide limited context on identity (e.g., recognizing a chair).

Summation of Inputs

• Process: Inputs from multiple sensors can be summed to form larger receptive fields.

Multiple Scales for Environmental Representation

• Strategies:

  • Use large receptive fields for identifying objects and ensuring position invariance.

  • Use small receptive fields for high acuity and detecting fine details of objects.

Topographic Maps in the Brain

• Definition: Orderly sensory space representation in which different neurons have receptive fields for distinct sensory spaces.

• Characteristics:

  • Neurons for nearby sensory spaces are spatially close in the brain.

  • Certain regions (e.g., fovea) dominate sensory maps for greater sensitivity.

• Brain Areas: Sensory spaces are mapped multiple times (e.g., visual areas like V1 and V2 each represent parts of visual fields).

Retinotopic Maps in Primary Visual Cortex

• Detail: The retinotopic map offers an orderly representation of visual space (hemifield), reflecting retinal organization.

Hemifield Representation

• Visual Maps: Multiple layers of retinotopic maps exist within visual brain areas, defining spatial representations for visual clarity.

Tonotopic Maps in Auditory Areas

• Overview: Tonotopic maps provide organized frequency representation of sound, ranging from high to low frequencies.

Somatotopic Maps in Somatosensory Areas

• Overview: Somatotopic maps orderly represent the body surface, indicating sensitivity across different body parts.

Advantages of Topographic Maps

• Efficiency: Grouped neurons reduce wiring and enhance interconnectivity for nearby sensory information.

• Connection Challenges: Neurons' connections within a map affect the representation of sensory information across all areas.

  • Coarse-grained maps facilitate better connections across distant areas.

Summary of Concepts

• Neurons and Receptive Fields: Neurons respond to specific parts of the sensory world.

• Dimensions and Types of Fields: Each type of sensory field (visual, somatosensory) provides specific modalities of information.

• Topographic Arrangement: Sensory information in the brain is organized into detailed and precise maps for improved processing.

Lecture 6: 2.6.25

Reference Frames

• Definition: A reference frame is a coordinate system that allows for the specification of an object's position relative to known points.

• Types of Reference Frames:

  • Egocentric:

    • Position relative to oneself.

    • Examples: Eye-centered, Head-centered, Body-centered.

  • Allocentric:

    • Position relative to external objects.

    • Examples: Object-centered, World-centered.

Understanding Positioning

• Positioning Context:

  • Meaningful only in relation to reference points (e.g., in a lecture hall, position might be specified relative to the lectern).

• Examples of Reference Frames:

  • Lectern-centered reference frame as the origin.

  • Use of Cartesian coordinate systems in mathematical contexts.

Neuronal Representation of Reference Frames

• Neurons utilize two broad classes of reference frames:

  • Egocentric:

    • Relative to the self (e.g., eye-centered, head-centered, body-centered).

  • Allocentric:

    • Relative to external entities (e.g., object-centered, world-centered).

• Receptive Fields (RF):

  • Neurons can be recorded to observe egocentric or allocentric representations based on movement and stimulus location.

  • If the RF moves with the observer, the representation is egocentric (e.g., eye-centered).

  • If the RF remains stable with respect to the environment, the representation is allocentric (e.g., world-centered).

Brain Areas and Mechanisms

• Hippocampus:

  • Primarily uses allocentric frames but starts with egocentric sensory information.

  • Responsible for creating allocentric spatial maps.

• Parietal Cortex:

  • Dominantly uses egocentric reference frames.

  • Interacts with the hippocampus for coordinate transformations during navigation.

• Retrosplenial Cortex:

  • Involved in transforming information between egocentric and allocentric frames, containing both types of cells.

Transformations and Head Direction

• Transformations:

  • Requiring head-direction information to combine egocentric data for allocentric representation.

  • Head-direction cells located in several regions, notably the anterior thalamus, inform spatial orientation independent of body position.

Interaction During Navigation

• Pathways connecting the parietal cortex and hippocampus support transformations between egocentric and allocentric frames.

• Parietal cortex provides egocentric data to the hippocampus for dynamic environmental mapping and assists locomotion planning.

Different Egocentric Reference Frames

• Types include:

  • Eye-centered: Coordinates adjusted based on gaze direction.

  • Head-centered: Coordinates relative to the head's position.

  • Body-centered: Coordinates for specific body parts.

Sensorimotor Transformations

• Process of converting visual target information to arm movement involves multiple transformations between reference frames.

• Information first perceived in eye-centered coordinates then remapped into body-centered coordinates to guide arm to the target location.

Examples of Coordinate Calculations

• T (eye-centered cup position) - H (eye-centered hand position) produces the hand-centered position of the cup.

• Two methods to arrive at hand-centered target location:

  1. Direct subtraction from eye-centered positions.

  2. Sequential transformation from eye-centered to body-centered coordinates.

Posterior Parietal Cortex's Role

• Coordinates transformations are managed in the posterior parietal cortex (PPC).

• Integrates visual and motor coordinates to facilitate accurate movements.

Summary of Reference Frames in Brain Function

• Reference Frame Types:

  • Egocentric (eye-centered, body-centered) and Allocentric (object-centered, world-centered).

• Different brain regions operate using specific reference frames:

  • Visual cortex: eye-centered

  • Motor cortex: body-centered

  • Hippocampus: allocentric

• Key Area: Parietal cortex crucial for coordinating transformations between frames.

Lecture 7: 2.11.25

Types of Synapses

• Axo-somatic synapse

  • Can have a relatively large influence on action potential generation in the post-synaptic cell.

• Axo-dendritic synapse

  • Likely the most common type of synapse.

• Axo-axonic synapse

  • Can influence transmitter release from the post-synaptic cell.

Synaptic Structure

• Synaptic cleft

  • The space between the pre-synaptic neuron and the post-synaptic neuron.

  • Approximately 20 nm wide.

• Synaptic vesicles

  • Contain neurotransmitters.

Neurotransmitters

• Chemical messengers that are sent across the synapse.

• Major neurotransmitter types:

  • Amino acids

    • Glutamate (Glu) – main excitatory neurotransmitter in the central nervous system.

    • Gamma-aminobutyric acid (GABA) – main inhibitory neurotransmitter in the cerebral cortex.

    • Glycine (Gly).

  • Amines

    • Acetylcholine (ACh), Dopamine (DA), Norepinephrine (NE), Serotonin (5-HT), Histamine, Epinephrine.

  • Peptides

    • Examples: Cholecystokinin (CCK), Substance P, Dynorphin, Enkephalins, and Neuropeptide Y.

Neurotransmitter Synthesis and Storage

• Nucleus

  • Location of neurotransmitter synthesis and storage.

• Rough ER and Golgi apparatus

  • Responsible for neurotransmitter processing.

• Synaptic vesicles

  • Each neuron generally contains only one type of amino acid or amine neurotransmitter and neuropeptides.

Neurotransmitter Release

• Steps in neurotransmitter release:

  1. Action potential travels to the presynaptic terminal.

  2. Synaptic vesicles are docked at the pre-synaptic "active zone."

  3. Action potential leads to an increase in pre-synaptic calcium levels.

  4. Calcium triggers neurotransmitter release from synaptic vesicles.

  5. Synaptic vesicle is recycled.

Calcium and Vesicle Fusion

• Calcium triggers vesicle fusion with the cell membrane:

  • SNARE proteins mediate fusion.

  • Synaptotagmin acts as a calcium sensor and activates fusion proteins.

• Binding of calcium (Ca2+) to synaptotagmin triggers fusion and transmitter release.

Post-Synaptic Receptors

• Two Classes of Post-Synaptic Receptors:

  • Ligand-gated Ion Channels

    • Neurotransmitter binds leading to ion channel opening.

  • G-Protein-Coupled Receptors

    • Neurotransmitter binding activates intracellular messengers, modulating ion channels.

Transmitter-Gated Ion Channels

• Characteristics:

  • Transmitters bind to receptors on channels initiating ion flow.

  • Contain two functional domains:

    • Extracellular domain with neurotransmitter binding sites.

    • Membrane-spanning domain forming the ion channel.

  • Produce rapid post-synaptic effects; changes in membrane potential within milliseconds.

Receptor Subtypes

• Different receptor subtypes for each transmitter:

  • AMPA receptor: ionotropic

  • NMDA receptor: ionotropic (transmitter-gated and voltage-gated)

  • GABAA receptor: ionotropic

  • GABAB receptor: metabotropic

Glutamatergic Ionotropic Receptor Subtypes

• Neurotransmitter: Glutamate

  • Agonists: AMPA, NMDA, Kainate

  • Includes metabotropic glutamate receptors.

Drug Influence on Synaptic Transmission

• Certain drugs bind to channels/receptors to affect synaptic transmission:

  • Examples:

    • Benzodiazepines (e.g., Valium)

    • Ethanol

    • Barbiturates

    • Neurosteroids

Synaptic Responses

• Post-Synaptic Potential (PSP)

  • Electrical recording of membrane potentials during synaptic transmission.

  • Affected by excitatory and inhibitory signals.

Excitatory and Inhibitory Post-Synaptic Potentials (EPSP and IPSP)

• EPSP

  • Produced by glutamate acting on AMPA receptors leading to depolarization.

• IPSP

  • Produced by GABA acting on GABAA receptors leading to hyperpolarization.

Synaptic Integration

• Spatial and Temporal Summation

  • Involves integrating multiple EPSPs and IPSPs to determine the overall potential affecting action potential threshold.

Synaptic Plasticity

• Definition: Changes in the efficacy of information transmission across synapses.

  • Includes changes in PSP magnitudes due to pre-synaptic action potentials.

• Types:

  • Short-term synaptic plasticity: Temporary increases/decreases (facilitation and depression).

  • Long-term synaptic plasticity: Linked to learning and memory (potentiation and depression).

Long-Term Potentiation (LTP)

• Definition: Increased EPSP response in post-synaptic neurons due to high-frequency pre-synaptic input.

  • Input-specific: Increased EPSP only at active synapse locations.

Mechanisms of Long-Term Potentiation (LTP)

• Mechanisms:

  1. Increased effectiveness of AMPA receptor through phosphorylation.

  2. Insertion of additional AMPA receptors into the synapse.

  3. Enhanced neurotransmitter release via retrograde messengers like nitric oxide.

Long-Term Depression (LTD)

• Definition: Decreased EPSP in response to low-frequency pre-synaptic activity.

  • Input-specific: Decreased EPSP only at active synapses.

Role of Calcium in LTP and LTD

• Calcium Levels:

  • Large increases in post-synaptic calcium lead to LTP.

  • Small increases induce LTD.

Summary

• Synaptic Transmission:

  • Action potentials trigger neurotransmitter release across the synapse, binding to receptors.

• Types of Post-Synaptic Potentials:

  • EPSP from glutamate and IPSP from GABA.

• Synaptic Plasticity:

  • LTP and LTD are mechanisms underlying learning and memory, influenced by calcium levels in pre- and post-synaptic cells

Lecture 8: 2.13.25

Different Types of Memory

• Declarative Memory

  • Involves the hippocampus and surrounding areas (medial temporal lobe; diencephalon).

  • Further divided into:

    • Semantic Memory: Knowledge of facts and concepts.

    • Episodic Memory: Memory of personal events and experiences.

• Nondeclarative Memory

  • Involves various brain structures:

    • Procedural Memory (skills and habits) – Striatum.

    • Emotional Responses – Amygdala.

    • Classical Conditioning.

Amnesia

• Retrograde Amnesia

  • Loss of pre-existing memories (things already known).

• Anterograde Amnesia

  • Inability to form new memories after the onset of amnesia.

Effects of Medial Temporal Lobe Damage

• Patient H.M.

  • Underwent surgical removal of substantial parts of hippocampus, perirhinal cortex, and entorhinal cortex to treat epilepsy.

  • Resulted in profound anterograde amnesia while procedural memory remained intact; no change in IQ, perception, or personality.

Medial Temporal Lobe and Declarative Memory

• Importance

  • Central role in declarative memory processing.

  • Location and connection of brain structures involved in memory formation, such as the thalamus and various cortices.

Role of Hippocampus in Memory

• Memory Storage

  • Uncertainty remains whether hippocampus acts as a temporary memory store or solely for indexing to retrieve stored memories in the neocortex.

  • Declarative memories are usually consolidated and stored in the neocortex, facilitated by interactions with the hippocampus.

• Memory Consolidation

  • Some studies suggest the hippocampus is essential for the initial consolidation of memories, particularly during the first few years post-learning.

Cortico-Hippocampal Circuits

• Functions of the hippocampus:

  • Supports episodic memory and spatial navigation.

  • Connects input from cortical areas to facilitate memory integration and processing.

Episodic Memory Defined

• Characteristics

  • Capacity for conscious recall of personal experiences and events.

  • Often described as mental time travel, allowing recall of specific experiences over time (e.g., sights and sounds).

Pattern Separation

• Memory Feature

  • The ability to distinguish and categorize similar experiences to prevent confusion.

  • Example: Remembering seating locations in lectures despite similar scenarios.

Pattern Completion

• Memory Feature

  • The capability to retrieve complete memories from fragmented cues or partial inputs.

  • Allows for recall even when context or cues are reduced.

Role of Hippocampus in Episodic Memory

• Binds inputs and enables retrieval processes, contributing both to pattern separation and completion.

Semantic Memory Defined

• Characteristics

  • Knowledge about the world, including facts and concepts.

  • Examples: Names and attributes of objects, historical data, cause and effect relationships, general knowledge about behavior.

Brain Networks for Semantic Memory

• Region activations seen in various brain areas during semantic processing (e.g., angular gyrus, fusiform gyrus).

Models of Semantic Knowledge

• Anterior temporal cortex may serve as an amodal hub facilitating communication between modality-specific regions.

Temporal Lobe and Category-Selective Cells

• Presence of neurons in the temporal lobe that respond specifically to different categories of information (e.g., face-selective cells in the inferior temporal cortex).

Multimodal Invariance

• Neurons show consistent response patterns regardless of how the object is presented (e.g., text, images).

Conscious Recognition

• Recorded neuronal responses indicating recognition capabilities in the medial temporal lobe.

Sparse Coding in Medial Temporal Lobe

• Specific neurons activated under recognition of distinct objects (like characters from Star Wars).

Synaptic Plasticity in Human Temporal Lobe

• Learning mechanisms observed similar to animal models:

  • High-frequency stimulation (LTP) and low-frequency stimulation (LTD) induce synaptic changes.

Summary of Findings

• Declarative memories are consolidated in the neocortex, highlighting the importance of both episodic and semantic memories.

• Temporal lobe contains neurons that represent categories and concepts, with synaptic plasticity being crucial for memory formation.

• The hippocampus plays a key role in episodic memory process but is not directly responsible for long-term storage.