How We Know What We Know Flashcards
Phrenology
Idea that bumps in the head tell us about how well developed different parts of the brain are (Pseudoscience)
Craniology
Linking things to the bumps in the skull
Organology
Idea that functions can be assigned to discrete places in the brain
Two factors to good Imaging technique
-Temporal Resolution
-Spatial Resolution
Lesions
Provide important information about what a part of the brain does
-Which abilities are lost
-Which abilities are preserved
-Not all lesions are accidental
Problems with Lesions
-Messy (Rarely restricted to one functional area)
-Plasticity can mask or alter effects
-Less obvious effect can co-occur (particularly if blood flow is impaired)
-There are rarely baseline (pre-lesion) measures for these individuals
Types of Neural Properties for brain imaging techniques
-Chemicals: Neurotransmitters or Ions
-Blood
-Electricity
-Magnetic Force (what creates electricity also creates magnetic force)
Patch Clamp
-Allows measurement of current flow through individual channels or whole cells
-Uses neurotransmitters
-Used for animals
-Spatial resoultion: 1 micrometer
-Temporal resolution: between 1 and 10 ms (5 ms?)
Single Unit Recording
-Micropipette is placed near but outside a neuron
-Action Potentials can be picked up
-Uses Electricity
-Animals/Humans preparing for brain surgery
-Spatial Resolution: between 10 and 100 micrometers
-Temporal Resolution: between 1 and 10 ms (5 ms?)
Intracranial Electrodes
-Some patients with epilepsy undergo neurosurgery
-Prior to surgery, electrodes are inserted through the skull, into the brain
-These are left in for at least a week
-During this time, experiments can be run on these patients
-Used for animals/humans preparing for brain surgery
-Uses electricity
-Spatial Resolution: 100 micrometers
-Temporal resolution: 1ms to 10ms (5 ms?)
Intracranial Electrodes Advantages
-Good temporal resolution
-Good spatial resolution
-Can get information for deeper structures
Intracranial Electrodes Disadvantages
-Incredibly invasive
-Only done with impaired population
-Location of Electrodes determined by clinical needs
-Few locations across patients
Functional Magnetic Resonance Imaging (fMRI)
-Used on Humans
-Uses blood
-High spatial resolution (1cm)
-Low temporal resolution (hundreds of milliseconds)
-Must avoid ferrous metals (iron-like metals attracted to magnetic fields)
-Even non-ferrous metals are problematic
-Very expensive
How fMRI works
-Oxygenated and deoxygenated blood have different magnetic properties
-When neuron start firing, they call up oxygenated blood
-This causes changes in the local magnetic field which can be “read” by the MRI machine
Critical Role of Subtraction in fMRI
-Lots of things always going on in the brain so how to identify what is active for your task and what is active for other reasons?
-Subtraction–compare activation under one condition with activation under another
-This is critical for getting meaningful activation patterns
Positron Emission Tomography (PET)
-First non-invasive method for obtaining localized functional data from neurological normal brains
-Uses radiation to follow blood flow
-Uses blood
How Does PET work?
-Brain consumes 20% of all oxygen in the body
-Oxygen can be radioactively marked and followed throughout the body and brain
-As radioactive oxygen decays, it releases neutrons
-Colliding neutrons form positrons that can be sensed outside body
Problems with PET
-Uses radioactive oxygen
-Has low spatial resolution (not as good as fMRI)(1-10cm)
-Has low temporal resolution (over a minute)
Electroencephalography (EEG)
-Uses Electricity
-Electric current is picked up by scalp electrodes
-These are then amplified
-When the electric signal is time-locked to a stimulus, the resulting signal is called an event-related potential (ERP)
Understanding ERPs
-By Convention, Up is Down and Down is Up
-Components named after their relative direction (positive or negative) and latency (how long after the stimulus they occur) in milliseconds
ERP Components
-P300: New Events
boop…boop…boop…beep…
-N400: Semantic violations
I like my coffee with cream and dog
-P600: Syntactic violations and ambiguities
The horse ran past the barn fell
-LAN: Syntactic Violations
The goose was in the ran
ERP limitations
-Can only get responses from cortex (problem for looking at A1 (primary auditory cortex) or deep structures
-Terrible spatial resolution (10 cm)
- but Great temporal resolution (100ms)
-Very noisy - need a lot of subjects
Magnetoencephalography (MEG)
-Uses magnets
-When neurons fire they create magnetic fields
-These can be picked up outside the head.
-Less distorted than electrical signal
-Better spatial resolution than EEG, same temporal resolution
Passive Techniques
-MEG
-EEG
-PET
-fMRI
-Intracranial electrodes
-Patch Clamp
-Single Unit Recording
Electro-Cortical Stimulation
-Uses electricity
-Humans preparing for brain surgery
-Spatial: 10 cm
-Temporal: 100 ms
-Neurosurgery patients awake for most of the procedure
-Able to give responses during this period
-Method by which homunculus for sensory and motor systems was determined
Electro-Cortical Stimulation Limitations
-Very Invasive
-Individuals undergoing procedure “not normal brain functioning”
-Processing area vs. part of circuit
Transcranial Magnetic Stimulation (TMS)
-Magnetic pulses sent through the skull
-Uses magnetic force
-Depending on properties of pulses, either activate or inhibit parts of the brain directly below the device
-These can work like temporary (reversible) lesions
-For humans
-Spatial: 10 cm
-Temporal: 100 ms
TMS Party tricks
-Make your toe wiggle
-Block your ability to name an object
-Create temporary short term memory deficits
