Cognitive Neuroscience: Brain, Neurons & Analysis

Cognitive Neuroscience

• Cognitive Neuroscience studies how the brain enables thinking, memory, perception, and decision-making
• It combines psychology and neuroscience to understand how mental processes work
• Scientists use brain imaging techniques like MRI and EEG to observe active brain areas during tasks

Level of Analysis

• Level of Analysis refers to studying a topic in multiple ways, each adding to the understanding

Neurons

• Neurons are responsible for creating and transmitting experiences and knowledge

Early Conception of Neurons

• Initially, scientists were unaware that the brain comprised billions of tiny units
• Early anatomists used stains to reveal a complex nerve net in brain tissue
• The initial belief was that the nerve net was continuous without stops, enabling free signal flow
• Early microscopes lacked the power to showcase small details
• In the 1870s, Camillo Golgi's silver nitrate staining made a few brain cells visible
• Ramon y Cajal later used Golgi's stain on newborn animal brains with fewer cells
• Cajal found the brain was not a continuous network, thus consisted of separate neurons
• Cajal's neuron doctrine posited individual neurons are fundamental units that communicate but are not physically connected
• This discovery overturned the nerve net theory, thus becoming a key neuroscience principle

Neuron Structure

• Cell Body (soma) is the neuron's metabolic center with mechanisms to keep the cell alive
• Dendrites branch from the cell body to receive signals from other neurons
• Axons (nerve fibers) are long processes that transmit signals to other neurons
• Neurons possess a receiving end and a transmitting end, as Cajal visualized, it was to transmit signals

Synapse

• The synapse is a small gap between one neuron’s axon end, and another neuron’s dendrites or cell body, where signals transmit

Selective Connections

• Neurons form specific connections, creating neural circuits instead of connecting randomly

Neural Circuits

• Neural Circuits are groups of interconnected neurons that work together for brain functions

Receptors

• Receptors are located in sensory organs like eyes, ears, and skin
• These receptors pick up and specialize in environmental information

The Signals That Travel Neurons

• Adrian recorded electrical signals from neurons using microelectrodes
• Small hollow glass shafts filled with a conductive salt solution pick up electrical signals at the electrode tip and conduct the signal to a recording device
• Modern physiologists use metal microelectrodes

Neuron Potentials

• Resting potential: A neuron at rest has a -70 millivolts (mV) resting potential
• It means the inside of the neuron is more negative than the outside
• The charge remains stable as long as the neuron is not sending a signal
• Action potential: Electrical signals travel down the axon of a neuron
• When stimulated, a nerve impulse travels down the axon, increasing the charge inside to +40 mV
• It lasts about 1 millisecond and after the impulse passes, the charge returns to its resting potential
• It is essential for transmitting signals within the nervous system
• Edgar Adrian found these signals maintain the same height and shape over long distances, as they move along axons
• When an action potential reaches the axon end, it triggers neurotransmitter release

Neurotransmitter

• Neurotransmitter is a chemical that allows the signal across the synapse (gap between neurons) and continues the journey
• Adrian connected nerve signals to human experiences, bridging neuroscience and cognition

Edgar Adrian's Research

• Edgar Adrian applied various levels of pressure to the skin to study how nerve firing relates to sensory experiences, also measuring neuron activity
• He found action potential shape and height remained the same, but the firing rate increased with stronger pressure
• It meant more intense stimuli caused neurons to fire more frequently, creating stronger sensations

Observed in Vision

• Brighter Light: It causes neurons to more rapidly fire
• Dim Light: It leads to slower firing
• This demonstrated the direct relation between neural firing rate and sensory experience intensity
• Adrian explored how different qualities of experience (such as color, movement, or shape in vision) are represented in the brain
• Action potentials look the same, therefore, distinct experiences are distinguished by activated neurons and brain areas they communicate with
• This concept founded understanding how the brain represents sensory experiences

Neural Representation

• The neural representation principle states that experiences are based on representations in the person's nervous system
• Adrian's research marks the study beginning of neural representation, relating high firing rate to increased pressure sensation

Neural Representation and Cognition Story

• Researchers in the 1960s recorded from single neurons in the primary visual receiving area, where Edgar Adrian's signals from the eyes first reach the brain
• They intended to determine which neurons fire in response to various visual stimuli
• Higher-level neurons in the brain respond to complex stimuli like geometric patterns and faces
• Neural firing is not limited to a single location, but distributed across multiple brain areas

Feature Detectors

• Researchers explored how nerve impulses represent different qualities of stimuli
• Early studies propose specific neurons might fire in response to stimulus features

Hubel and Wiesel

• In the 1960s, David Hubel and Thorsten Wiesel did experiments on cats, identifying neurons that respond to orientation, movement, or length
• This earned them the Nobel Prize in 1981
• Experience-dependent plasticity was confirmed to be one of the key research findings
• Brain structure’s change is based on experience
• Kittens that are born with feature detectors for various orientations, adapt to all orientations over time, as their brains grow
• Neural connections are shaped by experience, influencing perception

Blakemore and Cooper (1970)

• Blakemore and Cooper explored how experience shapes neural development by raising kittens in environments that contained only vertical or horizontal lines
• Kittens raised in the vertical environments responded to objects that were vertical and ignored the horizontal ones
• Kittens raised in the horizontal environments responded to objects that were horizontal and ignored the vertical ones
• Neurons in their visual cortex adapted to these specific orientations with little to no response corresponding to an absent orientation
• This experiment showed experience-dependent plasticity, which meant the brain adapts to its environment
• Further research contributed to comprehension of complex object representations in the brain, like trees
• Feature detection of trees involves detectors responding to specific parts, like vertical trunks and branches--similar to assembling Legos

Vision

• About 30% of the cortex is involved in vision
• Direct Signal: Some areas receive signals directly from the visual cortex
• Indirect Signal: Some process info via complex neural pathways
• Following Hubel and Wiesel's research on Feature Detection, scientists discovered that neurons in higher visual areas respond to complex stimuli (like lines or orientations)
• Instead of sole processing in the visual cortex, vision involves a wide network of regions that extract levels of detail (from shapes to objects)

Charles Gross Research

• In the late 1960s and early 1970s, Charles Gross & team experimented recording from single neurons in the monkey's temporal lobe
• Initial Testing, involving lines, squares & circles, failed to activate certain neurons
• Breakthrough, occurring with the shadow of the hand that fired one neuron
• Neurons in the Monkey’s temporal lobe specialize in recognizing complex objects like hands (meaningful shapes, rather than orientation/edges)
• Further Testing, that has shown the neuron respond best to the hand shapes featuring the fingers pointed upward

Perrett Research

• Neurons in visual cortex responds to simple bars
• Neurons in the temporal lobe respond to more complex shapes
• Other Neurons in the temporal lobe respond specifically to faces

Hierarchical Processing

• This is a lower level neuron that sends signals to the higher level where information is combined/refined for complex stimuli recognition

Grandmother Cell Theory

• Hierarchical Processing does not mean one neuron represents a whole object, like your grandma
• Instead, it is the multi-neuron group that forms the activity’s pattern

Sensory Coding

• It is the encoding of neuron characteristics present in the environment
• Researches have come up with 3 main theories on how objects are represented in the brain

Specificity Coding Theory

• It is the one-neuron firing in response to a specific object (like the "Bill neuron")
• This is unlikely because there are too many objects for the brain to separate each neuron in a brain

Population Coding

• When you have large number of firing neurons in a unique pattern that represents every single object
• Vast number of the objects to be represented
• Strong evidence to support the cognitive function

Sparse Coding

• This small group of firing neurons in a pattern that represents every single object, with the neurons all remaining inactive
• Neurons that respond to most objects with a distinct active pattern of activity
• Recent studies have found neurons in the temporal lobe that respond to specific stimuli, supporting coding’s specialized representation

Quiroga (2007) Research

• Quiroga found neurons that responds to specific faces such as Steve Carell even, but later suggested additional ones
• It supports the Sparse Coding (small neurons that fire various patterns)

Olshausen & Field (2004) Research

• This study indicated how visual objects or sounds/ odors is likely by coded sparing, where only a few active neurons do the perception

Perception

• The real-time response neuron firing to environmental stimuli
• Neural Firing retrieves stored information representation from past experiences
• Exact nature of neural representation in memories has not been fully understood, like sparse coding principles to trigger unique neural firing

Representation

• To grasp cognition in the way it operates, the researchers have to examine the brain organization for how brain functions and neurons are structured within different brain regions

Representation Localization

• It suggests the responsible regions in the brain are specific for it's own functions
• The cerebral cortex (thin, wrinkled layer) handles cognitive functions and subcortical areas (or the areas below) are responsible for the functions

Paul Broca (1861)

• Paul research that found from patients with the damage in the brain area that came from strokes determined Broca’s area which was responsible for speech production

Broca's Aphasia

• Damage here causes slow, labored, grammatically incorrect speech

Carl Wernicke (1879)

• Carl dentified Wernicke’s area in the temporal lobe, that found how damage is made to that area causes speech fluent/ incoherent & the inability to the understand language & causing aphasia

Understanding

• His findings were demonstrated how language comprehension and production are placed within all the distinct brain regions
• It has laid the background/ groundwork idea for each other’s functions

Further Evidence Studies

• This came from the wartime brain injury that showcased predicable deficits by damaging occipatal lobe damage

Other Regions Studies

• Like with the cortex area and somatosensory area has all linked the sensory functions too

Prosopagnosia

• Temporal Lobe damage can cause this to individuals where they don’t recognize faces at all
• Cortical Equipotentiality, a thought to take in the 1800s, suggested if functions of the brain operated altogether as part of specialized areas

Demonstrating Double Dissociation

• Modern Researches that suggests the areas for specialized or certain or specific functions have certain patient cases just for these functions to establish what's double or what’s ensuring something that's specialized

Brain Dissociation

• Brain Dissociation occurs when an area in the body impacts A, while just leaving the B function

Functions Research

• These have all been shown to be cases for object and facial recognition
• Localization of functions can be made easier with single-cell or single-neuron recording, in a method

Tsao Research

• Doris Tsao and team found 97% of monkey neurons responded when shown pictures of faces
• Human's "face area" can show in its respective region nearby the prosopagnosia regions
• Studies in the brain imaging show this brain area that have certain cognitive functions activated

Functional Magnetic Resonance Imaging (fMRI)

• fMRI is when you the researchers measure how an active brain and all that's measured is with changes with the blood and certain oxygen levels
• Once the active neurons have done their work that means they’re working with more oxygen levels which in turn binds to the hemoglobin within the blood
• It increases the magnetic properties made to hemoglobin, giving them power or leading fMRI’s to become really powerful

Voxels

• This small brain activity used for analysis is put directly for fMRI experiments in the shape or units of cubes or the range of 2-3mm
• Brain activity maps with 3D and changes in color (increased decreased activity representation) are made easier due to use of voxels for statistical procedures