Lecture 1- What is cognitive neuroscience? Flashcards
What is cognitive neuroscience?
The study of the biological processes underlying cognition
What are neuroscience methods?
- Neuroanatomy
- Invasive neurophysiology: measurements from inside the brain
- Non-invasive methods: measurements of brain activity made from outside the brain
- Computer simulations
What is meant by temporal resolution?
the precision of measurement of brain activity in time
What is meant by spatial resolution?
the precision of measurement of brain activity with respect to space
What is meant by invasive techniques?
the degree to which the brain is directly and physically affected by the technique
What does the hypothalamus do?
Regulates functions that are essential for maintaining the normal state of the body (homostasis) and reproduction. Controls hormone release
What is the thalamus?
Relay station in the pathways from sensory receptors to the cortex
What does the brainstem do?
Connects the cerebrum with the spinal
Cord, carrying signals between the rest of
The brain and the body
What is the cerebellum related to?
Sensorimotor control and learning; other cognitive functions such as language
What does the cerebral cortex do?
Integrates information from across the brain and is the seat of most cognitive functions
Awareness, perception, memory, attention, planning, language, emotions, consciousness.
What connects the hemispheres?
The corpus Callosum
What separates the two hemispheres?
Longitudinal fissure
What are gyri?
The ridges of the brain
What are sulci?
The grooves of the brain
What is the gyrus surrounded by?
Two sulci
What is a very deep sulcus?
A fissure
What are the two main fissures?
Central fissure
Lateral fissure
What are the location descriptors of the brain?
Anterior
Dorsal (Top)
Ventral (Bottom)
Medial –>
What is computed tomography?
An early method of studying the brain which creates a 3D reconstruction of the brain .
It has a relatively low resolution (1cm)
What is Magnetic Resonance Imaging (MRI) ?
- Essentially measures the presence of water in the brain
- Specifically: the protons making up the nucleus of the hydrogen atom in H20
- A combination of strong magnetic field + ratio pulses leads to protons emitting radio signals
MRI picks up these radio waves
What to MRI images show?
High-resolution structural images that show Grey matter (made of cell bodies "processors") White matter (axons "cabling")
What is Diffusion Tension Imaging (DTI)?
- A variant of MRI
- MRI can be tuned to detect diffusion (movement) of water, diffusion in the brain is anisotropic (restricted)
- Myelin sheath surrounding axon produced a tight lipid (i.e. fatty) boundary
- Water diffusion is greatest in axons
- Reveals long range connections
- High resolution structural images of long-range axons running in white matter (so called tracts)
What are lesion studies?
- Historically the oldest method of cognitive neuroscience (Broco, Wernicke)
- Damage to the brain area leads to cognitive impairment
What are the pros and cons of lesion studies?
Pros:
- Artificial ablations are
precise (usually in animals)
- Unequivocal evidence that damaged area participates in certain cognitive function
Cons:
- Spatially imprecise when caused by injury when caused by injury or disease
- Does not reveal fully how or where function takes place
What are single and multi-cell reocrdings?
Extracellular recordings of action potential from one or many cells
Usually in animals: visual and auditory processes
In humans, occasionally: electrodes implanted in epilepsy patients
What increases local blood flow to blood vessels in the brain?
Neural activity increases local bloodflow (with delay)
What is Positron Emission Technology (PET)?
- Measures changes in blood flow
- Usually between control and experimental condition
- Radioactive isotope injected into blood
- As isotope decays, it generated gamma rays (photons) which the PET instrument detects
What is Functional Magnetic Resonance Imaging (fMRI)?
- Indirect: measures blood flow with same principle as MRI
- Blood Oxygenation Level Dependent (BOLD) Signal
- Sluggish: response peaks several seconds after stimulus onset
What are the pros and cons of PET and fMRI?
Pros:
- Good spatial resolution : PET: 1cm voxels (i.e., 3D pixels) fMRI: 3-6 mm
- Access to all parts of the brain
Cons:
- Poor temporal resolution: PET 1 min, fMRI 5 seconds
- Indirect: measures blood flow rather than neural activity directly
What do electroencephalography (EEG) and Magnetoencephalography (MEG) do?
Measure neural activity directly
What is the pyramidal cell?
- The majority of cortical cells are pyramidal cells
- Their main feature is the apical dendritic tree
- Pyramidal cells are logically aligned with each other
What is the electrical circuit of the pyramidal cell?
Synaptic currents: positive ions flowing into dendrite
Primary current: current flowing along dendrite
Leak current: current leaks out along the dendrite
Secondary (volume) current: completes the circuit
How are cortical cells organised?
Cortical cells are organised into columns, with multiple aligned apical dendrites, perpendicular to cortical surface.
Signal entering a column activates all the cells in the column
Cells within a column are synchronously active.
How are currents of cortical cells summed?
Nerve cells seldom become active alone.
Nearby cells and columns tend to become synchronously active
A large number of aligned pyramidal neurons in columns sums up to large primary and volume currents.
EEG/MEG reflect these currents and the activity of neural masses.
What is the basic physics behind EEG/MEG?
- Positively charged ions repel each other
- Electric charge is proportional to number of ions
- If two regions have unequal charge, there is electric potential between them.
Connecting the regions causes electric current. This measures the electric potential - Electric current causes a magnetic field around the current (Maxwell’s equations)
- The right-hand rule gives the relationship between the current and the magnetic fields
- Primary currents in the brain cause magnetic fields. This is measured in MEG.
What other techniques are closely related to EEG?
- Electrocoticography (ECoG): electric field potential measurements from the cortical surface
- Local field potential (LFP): electric field potential measured from inside cortex
What activity does MEG pick up?
- MEG picks up cortical activity, but very little from deeper in the brain.
- MEG “blind” to activity in gyri.
It is sensitive to primary currents in sulci
EEG and MEG Oscillation Bands
- Both MEG and EEG show oscillatory activity in different frequency bands
- Cognitive and arousal states are associated with characteristic oscillations
Correlations between oscillations in different cortical regions reveal functional connectivity maps of the brain.
Time Frequency Analysis (TF)
- EEG/MEG signals contain many frequencies that change during a cognitive task
- The amplitude of an oscillation is its power
You can code power as colour, e.g. high amplitudes in red, low in blue - TF analysis is plotting power in time-frequency plane.
Where do you measure MEG/EEG from?
The surface of the scalp= far away from brain activity
What are the problems of localising activity with EEG and MEG?
- EEG/MEG responses do not directly reveal locus of generation
- Forward problem: calculate field pattern when primary current (sources) known.
- Inverse problem: calculate primary current from field pattern.
What are the solutions for the problems with EEG and MEG?
- Simplifying assumptions: assume the primary current is a single point (dipole)
- Constrain solutions to the cortex on the basis of MRI
Constrain solutions to activity map given by fMRI
What are the Pros and Cons of EEG and MEG ?
Pros:
- Very good temporal resolution (1ms)
- Quite good spatial resolution
- Can be combined with other techniques
Cons:
- MEG sensitive to current orientation
- MEG doesn’t see deep sources
- Localization difficult and uncertain
- EEG worse spatial resolution than MEG
What are examples of Invasive Perturbations?
Cortical Cooling
Pharmacology
Direct Electrical Stimulation
Optogenetics
Are invasive perturbations possible to use on humans? And what are some methods?
Yes
Direct stimulation
Drug research
How are invasive perturbations used in epilepsy?
- Direct stimulation used for mapping speech areas of epilepsy patients, to avoid these in operations to remove parts of cortex.
What are non-invasive methods
- Transcranial magnetic stimulation (TMS)
- Transcranial direct-current stimulation (tDCS)
What is Transcranial Magnetic Stimulation?
- Electric current in coil generates magnetic field
- Magnetic field generates focal electric field in brain
- This field depolarises neurons locally
- This interferes with cognitive processing
What are the Pros and Cons of TMS?
Pros:
- Good temporal (10ms) and spatial (10 mm) reolsution
- Harmless- acts like temporary lesion
- Subjects act as their own controls
Cons:
- Cortical effect: doesn’t reach deeper brain areas
- Neurophysiological effect not clear
What is Transcranial Direct Current Stimulation (tDCS)
- In this method, positive, low-level current is induced between two electrodes: the anode and the cathode
- This results in depolarization and action potentials under the anode
- Hyperpolarization (inhibited activity) under cathode.
What are the pros and cons of t(DCS) ?
Pros:
- Cheap, portable, safe
- Subjects act as their own controls
- Clinical applications (e.g., depression, Parkinson’s)
Cons:
- Poor spatial and temporal resolution
- Cortical effect: doesn’t reach deeper brain areas
- Neurophysiological effect not clear
What technique would you use to get high spatial resolution?
fMRI, PET
To see which networks are performing cognitive task
What are the perturbation methods and what do they do?
TMS and tDCS
They . test if specific region is part of network performing task
What are high temporal resolution methods and what do they do?
MEG and EEG
To find out the time in order of events of the brain
