Cog Sci 3 - What Can We Learn from The Brain?

What are the structures of a neuron?

• Dendrites

• Soma

• Axon

• Axonal Terminals

Dendrites

Branch like structures that expand from the cell body that receive signals from other neurons

Carries signals to the cell body

Soma

Cell body and acts as a control center

Contains the nucleus and DNA
Handles metabolic processes and protein synthesis

Axon

Long thin fiber that carries electrical impulses from the soma to the axon terminals

Axon Terminals

End branches of axon that releases neurotransmitters to communicate with adjacent cells

Synapse

Gap between neurons

How do neurons connect to each other?

Neighboring neurons send and receive signals through a combination of chemical and electrical signals

Signals are transmitted from one neuron to the next via SYNAPSES

Each neuron is connected to about ten thousand other neurons

Neurotransmitters

Chemical Signals

Action Potentials

Electrical Signals

Cortex

Outer layer

Recently evolved

Higher level cognition

Gyri

Ridges in the cortex

Sulci

Valleys of the cortex

How is the cortex divided?

Into 2 hemispheres: right hemisphere and left hemisphere

What are the 4 Lobes?

Frontal

Temporal

Parietal

Occipital

Frontal Lobe

Problem solving and language production

Temporal Lobe

Auditory Processing and language comprehension

Parietal Lobe

Attention and spatial processing

Occipital Lobe

Visual processing

Subcortical Structure

Inner formations that are found in all vertebrates

Methods of Cognitive Science

• Causal/Interventionist Methods

• Observational/Correlational Methods

Types of Causal or Interventionist Methods

1. Lesion-deficit method

2. Brain stimulation methods —→ Transcranial Magnetic Stimulation (TMS)

Types of Observational or Correlational Methods

1. fMRI imaging

Lesion Deficit Method

Connects specific areas of brain damage to missing physical or mental abilities in order to figure our what those brain parts do

Lesion

An area of damaged tissue, due to an injury or stroke

Deficit

the loss of a specific function or behavior

Example of Lesion-Deficit Method

Phineas Gage who experienced change in personality after damage in his left frontal lobe

What are the limits of lesion-deficit studies?

1. Brain damage isn’t precise

2. Brain damage isn’t replicable

How is brain damage not precise?

No two lesions are the same

Swelling of the lesion can affect neighboring areas

Wy does it matter that brain damage isn’t replicable?

Limits the subject pool

There is no record pre-damage behavior

What discovery did lesion deficit method lead to?

The function of several brain regions, such as Broca’s area

Broca’s Aphasia

Slow, laborious, non-fluent speech

Comprehension is relatively intact

Broca’s area found in the front of the head

Who discovered Broca’s aphasia?

Paul Broca

Wernicke’s Aphasia

Fluent but disordered speech

Impaired comprehension

Wernicke’s area is found in the back of the brain

Who found Wernicke’s Area?

Carl Wernicke

Functional Specialization

Different areas in the brain are specialized for different functions

What did lesion deficit method contribute to?

It contributed to our understanding of functional specialization

TMS

Transcranial Magnetic Stimulation

Uses magnetic fields to stimulate nerve cells in the brane

Non-invasive: doesn’t use surgery or cutting of the skin

Limits of TMS

1. Cannot isolate deep, subcortical brain regions such as hippocampus or amygdala

2. Not spatially precise as the current can diffuse

fMRI

Functional Magnetic Resonance Imaging

Shows activity in the brain as subject is stimulated or doing something

How do fMRIs work?

BOLD Signal and Subtraction Method

BOLD Signal

Blood Oxygenation Level Dependent

Oxygen is needed for an area of the brain to become active

Subtraction Method

During fMRI, activity in response to a stimulus is compared to baseline activity

Brain Scan during stimulus - Brain scan during rest = what part of the brain is actually active during test

Brain is still active during rest

What does fMRI provide evidence for?

Functional Specialization

What functional specialization is connected to fMRI?

Fusiform Face Area (FFA) and Visual Word Form Area (VWFA)

Fusiform Face Area (FFA)

Area of visual processing that specializes in facial recognition

The size and exact location of the FFA vary from person to person

Who discovered FFA?

Nancy Kanwisher

Visual Word Form Area (VFWA)

Area of visual processing that specialized in written language

Limitations of the evidence for functional specialization for fMRI

FFA still demonstrates activity even for other stimuli other than faces

Blind adults use visual cortex to process language

This is due to brain plasticity as the connections that aren’t used will be used for something else

What are the limitations of fMRI regarding information and the causal role?

fMRI doesn’t tell us what information that the region represent

fMRI doesn’t tell us the causal role of a region’s response in behavior

What is the Parvizi et al. (2012) study?

Study of an epilepsy patient that received direct intracranial electrical stimulation alongside an fMRI. The implantation covered the right inferior/ventral temporal region of the brain.

During stimulation, the patient had distortion in the visual experience of faces. There were NO distortions in his visual experience of non-face objects.

There were no distortions when stimulating other nearby brain regions

Why would fMRI struggle to show the causal roles of brain areas?

fMRI merely shows correlations. It doesn’t modulate or intervene on brain activities which is why it cannot show causal relations

What do researchers debate about how faces are perceived and processed?

They debate if faces are represents as a holistic entity or a piecemeal manner?

Holistic Manner of face processing

Represent the face with structural features like the distance between faces

Piecemeal Manner of face processing

Represent the face simply as a combination of different facial features (e.g. eyes, nose, mouth)

What manner explains the face inversion effect?

Holistic representation: our processing is disrupted when a face is turned upside down because when upright, the face is percieved as a unified whole (GESTALT)

When inverted, our brain switches to a slower, piece by piece feature analysis

What did the study of Gold et al (2012) show us?

A face is perceived no better than the sum of its individual parts

fMRI would struggle to tell us about what kind of representation our mind generates and uses in its computations

Behavioral methods can shed some light on questions about representation by comparing participants’ performance under different conditions

Computational methods used in cognitive neuroscience

• Computational Analysis

• Computational Modeling

Computational Analysis

Understand brain pathways and networks

Computational Modeling

Simulate neural activities and make predictions about the functions of neurons

What is the Shapson-Coe et al study?

Reconstruction of adult human temporal cortex at nanometer resolution

Cut the tissue into 5,019 serial sections

Imaged sections using multibeam scanning electron microscopy

Computationally aligned the images and used machine learning to segment cells and detect synapses

Connectome

3D image of nearly every neuron and its connections within the sample

Classification and Detection are imperfect so it is not error free

Limitations of the Connectome

Connectome tells us the wiring of a brain region BUT it doesn’t tell us about

• activities in that region

• What function it performs and how it performs its function

Connectome + Mapping Fly’s Visual System

Using the existing connectome data as architecture constraint, a model of the fruit fly’s visual system was created and trained to detect motion

The model reproduced several well established features of the fly’s motion-vision system such as the division of labor between neuron types

Significance of Mapping Fly’s visual system using connectome data

It makes predictions about the functions of neurons

Split Brain

Disconnection between the left and right hemispheres of the cortex

What method is Split Brain an example of?

Lesion Deficit Method

What is the organization of split brain?

Contralateral Organization:

• Left Brain controls the right body

• Right Brain controls the left body

What does split brain show us?

Functional Specialization

• Where functions are localized such as where verbal processing is localized

• How functions may be split across separate sub systems