introduction and neuroimaging Flashcards
mathematical model
The use of mathematical language and equations
to describe psychological and/or neural processes.
computational model
The use of mathematical language and equations to describe steps in psychological and/ or neural processes (often implemented on a computer).
efficient coding models
Theoretical and/or computational models that
explain neural processing by assuming that sensory systems become tuned to predictability in natural environments in ways that economically encode predict- able sensory inputs while highlighting inputs that are less predictable.
bayesian models
Theoretical and/ or computational models that employ Bayesian statistical methods to gen- erate an internal model of the source of sensory inputs based upon prior experience.
predictive coding
The use of Bayesian models to predict future inputs. If pre- dictions do not match inputs (prediction error), the model is adjusted to improve future predictions.
artificial neural networks
Also referred to as connectionist models,
are computational methods that consist of networks of nodes with weighted connections between them. Connection weights increase and decrease following experience in ways that resemble orga- nization of biological neural networks
deep neural networks
Artificial neural networks that have a very large num- ber of layers of nodes with millions of connections.
What’s the difference between sensation and perception?
A similar distinction:
Sensation is the immediate, basic experience generated by external stimuli.
Perception involves the interpretation of these sensations, giving them meanings and organization.
No clear boundary-fuzzy distinction
Think of sensation as the initial processing carried out by our sensory systems and perception as the interpretive processing of this sensory information
Cajal
Cajal- made drawing of organization of neurons in the brain.Neurons do not actually touch( separate cells with tiny gaps(synapse))
Loewl
Loewl-excitatory( increase response of next neuron). Inhibatory( decrease response response of next neuron)
Chemical instead of electrical NT travel from axon across the synapse to bind to receptor molecules on the dendrite of the next neuron - some excite or inhibit from firing
Neuroimaging
A set of methods that generate images of the structure and/or function of the brain.
Allow us to examine the brain in healthy, living, behaving humans.
Dendrite
Receives info
Soma
Contains nucleus & multicell organelles
Terminal
Synapse with target cell
Axon
Conducts AP away from cell body
Axon Hillock
Info integrated here.
Generates AP
Types of structural NeuroImaging Technologies
Structural techniques:
Computerized Tomography(CT)
Magnetic Resonance Imaging(MRI)
Types of functional NeuroImaging Technologies
Functional techniques:
Functioning Magnetic Resonance Imaging(fMRI)
Positron Emission Tomography(PET)
Electroencephalography(EEG)
Event-Related Potential(ERP)
Magnetoencephalography(MEG)
Advantages of MRI over CT
Higher resolution(clearer images)
No radiation
Versatile
Advantages of CT over MRI
Advantages of CT over MRI:
Advantages of CT over MRI:
More comfortable environment
MRI is very loud
No danger of asphyxiation
No danger of foreign materials
How can we determine function?
(B❤️H)
Metabolic imaging: indirect measure of brain activity
based on changes in blood flow
Functional MRI (fMRI)
Positron Emission Tomography (PET)
Electromagnetic:direct measure of brain activity
Electroencephalography (EEG), event-related potentials (ERPs)
Magnetoencephalography (MEG)
Metabolic Imaging: The Timecourse of Blood Flow
Changes in cerebral blood flow (CBF) are very slow.
Typically 5-20 seconds post-stimulus.
Consequently, metabolic imaging techniques suffer
Functional magnetic resonance imaging (fMRI)
Blood oxygen level-dependent (BOLD) signal:
The ratio of oxygenated to deoxygenated hemoglobin that permits the localization of brain neurons that are most involved in a task.
Active brain tissue needs oxygen. Which is delivered by blood( active brain demands more).
See the activity of the brain.
Temporal resolution is slow.
Machines noisy,expensive.
Looks at increase metabolic activity
Positron emission tomography (PET)
Small amount of safe, biologically active, radioactive material( a tracer) is introduced in the participants bloodstream.
Camera directs gamma rays emitted from brain region where the tracer is being used the most.
Advantages of fMRI
Slightly higher spatial resolution
Does not require a radioactive tracer
Advantages of PET
Different radioisotopes provide more flexibility for PET
Radiopharmacology
The Subtractive Approach
All parts of the brain are active at all times
Interested in small changes in blood flow during cognitive processes
Need to use a good control condition to isolate the cognition-related activity
Example of Subtractive Approach- Peterson, Fox, Posner, Mintun, & Raichle (1989) -Experimental conditions
1) Subjects stared at a crosshair on a computer monitor while their brain activity was monitored via PET imaging
2) Common English nouns appeared on the screen (visual), or were heard over earphones (auditory). The presentation rate was 40 words a minute.
3) The subjects were asked to speak the words that they saw or heard.
4) The subjects were asked to say aloud a use appropriate for the noun they either viewed or heard (e.g., if the word was ‘hammer’ an appropriate response would be ‘hit’)
Example of Subtractive Approach-Subtractions
Hearing words: Condition 2 (Auditory) – Condition 1
Seeing words: Condition 2 (Visual) – Condition 1
Speaking words: Condition 3 – Condition 2
Generating words: Condition 4 – Condition 3
Electroencephalography (EEG)
Measures brain electrical
activity at the scalp from
the rapid post-synaptic potential changes of of pyramidal cells in the cortex
Dozens of electrodes on the scalp
Can’t learn what individual neurons are doing or pinpoint exact are of neural activity
Localize population of neurons and measure their activities with excellent temporal accuracy
MRI
Uses responses of atoms to strong magnetic fields to form images of structure in the brain
Event related potential (ERP
Created by averaging together many EEG trials time locked top a specific event
Tells us about temporal processing of a stimulus
Magnetoencephalography MEG
A technique similar to eeg that measures changes in magnetic activity across populations of many neurons in the brain
Has the same high temporal resolution as EEG, but better spatial resolution
Provides good measure of neuronal timing
Shows where in the brain neurons are. Most active
Shows that very small changes in local magnetic fields accompany the small electrical changes that take place when a neuron fires - use small devices to measure these tiny magnetic field changes
Simple and cheap
EEG vs Meg
EEG:
Relatively inexpensive
Portable
Equivalent:
Safe/non-invasive
Very high temporal resolution (1 ms accuracy)
MEG
Better spatial resolution (though not as good as fMRI)
