Brain Sciences 4 Flashcards
fMRI process
fMRI
1st level - predicting time series and parametric modulation
Theoretical model: In each participant and in each voxel, the time course of the BOLD signal is generated by:
Onset of event → modulation of neuronal activity by cognitive variable (model based SV) → neuronal activity leads to hemodynamic response function using convolution to get closer to BOLD signal → adding observation noise → observed signal → We use regression analysis to revert this process
Regression independent for each voxel. One beta per participant and voxel. Map of betas per participant.
2nd level - analysis across participants: getting a combined statistical parametric map that takes into account all individual participants maps. Check whether data matches prediction.
Beware of false positives when doing this (some noise might pop up as significant). So need to correct for multiple comparison problem.
Solution: raise significance level. Divide p-threshold by amount of tests. Or use FWE which takes into account that nearby voxels are related.
EEG/MEG process
- Neocortex cortex is divided into layers with many synapses where EPSPs occur.
- AP from presynaptic neurons releases glutamate.
- Glutamate binds into post-synaptic neuron which trigger an EPSP.
- If many EPSPs occur simultaneously, an electrode placed on the surface the head can detect the electric fields caused by the neuronal activity.
- EEG can detect electric fields and MEG detects magnetic fields (as a result of the dipole from electrical activity) caused by neuronal activity.
- Preprocess data: epoching, artificat removal and filtering frequencies we are not interested in.
- Event is the stimulus of experiment. Average out all the trials to get ERP (event-related potential). High temporal resolution: we can see changes in the brain by the millisecond.
- M/EEG signals are composed of several frequencies. With a Fourier transformation, you can do a frequency decomposition of the signal, which tells you how strong the oscillations are for each frequency band.
- Brain activity can be expressed in a time-frequency plot (moving your finger example).
● Power: contribution of that frequency at that time point to the signal
● An increase in power means: event-related synchronization of brain activity (the brain
area oscillates). - Inverse problem: there are an infinite amount of sources from within the brain that could be responsible for the data detected. Hence, use sophisticated mathematical techniques and realistic information about the individual’s brain (e.g., with an MRI scan), the source of the signal can be estimated
Note: When brain activity from a large ensemble of neuron starts to display
repetitive, rhythmic patterns, we observe oscillations outside the skull
● Synchronization of brain activity gives stronger oscillations, desynchronization
gives weaker oscillations
● Waves have a certain frequency, which we categorize in bands
What is the most direct way to process visual information?
Visual information from the outside world is processed by multiple layers of cells in the retina and transmitted via the optic nerve to the thalamus, and from there to V1—a pathway often referred to as the retinogeniculostriate or primary visual pathway where the information begins to be processed.
What about auditory information?
Neural projections from the cochlea (the auditory sensory organ in the inner ear) proceed through the subcortical relays to the medial geniculate nucleus of the thalamus and then to the primary auditory cortex. The auditory cortex has a tonotopic organization, meaning that the physical layout of the neurons is based on the frequency of sound.
Important info about glutamate
Glutamate is released by the pyramidal cells of the cortex, the most common cortical neurons. As a result, glutamate is the most prevalent neurotransmitter and is found in most of the fast excitatory synapses in the brain and spinal cord. A few different types of receptors bind glutamate, and some of these are found in modifiable synapses (i.e., ones that can change in strength) involved in learning and memory.
Too much can be toxic and cause cell death and has been implicated in stroke, epilepsy, and neurodegenerative diseases such as Alzheimer’s and Parkinson’s.
GABA
GABA is the second most prevalent neurotransmitter and is synthesized from glutamate. It is found in most of the fast inhibitory synapses across the brain. As with glutamate, there is more than one type of GABA receptor, but the most common one opens Cl2 channels to allow an influx of negatively charged ions into the cell, negatively shifting (hyperpolarizing) the membrane potential and, in essence, inhibiting the neuron by making it much less likely to fire.
Decreased levels of GABA (decreased inhibition) can result in seizures, as well as increases in emotional reactivity , heart rate, blood pressure, food and water intake, sweating, insulin secretion, gastric acid, and colonic motility . Too much GABA can lead to coma.
Serotonin information
Serotonergic pathways are involved in the regulation of mood, temperature, appetite, behavior, muscle contraction, sleep, and the cardiovascular and endocrine systems. Serotonin also has effects on learning and memory. Drugs such as the selective serotonin reuptake inhibitors (SSRIs), used to treat clinical depression, act on the raphe nuclei and their targets in the brain.
Dopamine
The primary sites of dopamine production are the adrenal glands and a few small areas of the brain. Brain areas with significant dopaminergic innervation include the striatum, substantia nigra, and hypothalamus. There are several dopaminergic pathways, each sprouting from one of the small brain areas where it is produced and each involved in particular functions, including cognitive and motor control, motivation, arousal, reinforcement, and reward, among others. Parkinson’s disease, schizophrenia, attention defi cit hyperactivity disorder, and addiction are associated with deficits in dopamine systems.
Optogenetics and give example
Genes are modified so neurons build a protein that forms light sensitive ion channels in the neuron
● When light on an implanted LED is turned on, the ion channels open
● This affects firing of the neurons, which affects behavior.
Behavioral changes resulting from optogenetic stimulation of cells in a subregion of the amygdala.
- When placed in an open, rectangular arena, mice generally stay close to the walls (left).
- With amygdala activation, the mice become less fearful, venturing out into the open part of the arena (right)
