HC1 Introduction Flashcards
Cognitive neuropsychology
The study of the relation between structure and function of the brain and specific cognitive functions (e.g. language, memory, attention, …)
Cognitive neuropsychology research
- By investigating these cognitive processes in normal healthy people.
- By investigating the breakdown of these processes in brain-damaged individuals (as a result of acquired brain damage or as a result of a developmental disorder).
Brain enthusiasm
- Brain scans as evidence in court of law
- Brain scans might be overinterpreted by laypersons.
- Good progress for several neurological syndromes, but less progress for psychiatric and mental syndromes.
Neurons
Contain with cell bodies in grey matter of cerebral cortex and subcortical structures
Axons
Contained by white matter
Neuron without input
Without input (at rest), cell membrane of a neuron has
an electrical potential difference between in- and outside of -70 mV
Post-synaptic potential
Is determined by integrating input of many synapses at the dendrites. It can hyper and depolarize.
Neural communication
o Input neurons (through neurotransmitters): action potentials over time
→ Membrane potential of post-synaptic neuron depolarizes or hyperpolarizes
o Over time, membrane potential of post-synaptic neuron changes in function of input it receives = signal
Simplest signal
Sinusoidal oscillation
Frequency
Rate of change of signal, e.g. in the time dimension
o 1 Hz = completing a full cycle (going up & down) in one second
o Biological signals never contain just one frequency
Complex signals can be decomposed into..
Frequency components
Each has a particular frequency (e.g., 1 Hz, 2 Hz, 3 Hz, …)
Amplitude
How much it goes up and down
Phase
When it goes up and down
Frequency spectrum
Measured range of frequencies
Highest frequency
▪ Limited by sampling frequency
▪ ½ * sampling frequency (Nyquist sampling theorem)
Lowest frequency
▪ Limited by how long the signal is measured
▪ 1 / number of seconds measured
Filtering
Attenuating or excluding certain part of measured frequency spectrum (low-pass, high-pass or band-pass)
Spectrogram
Strength of each signal component at each moment in time
Electrophysiological changes are connected to other kind of changes: at a SMALLER scale
Movement of chemical substances and molecules
▪ E.g. depolarization: influx of Na+, repolarization: outward current of K+
▪ E.g. calcium concentration high in electrically active neurons → two-photon calcium imaging
Electrophysiological changes are connected to other kind of changes: at a LARGER scale
Hemodynamics
▪ Blood supply is adjusted to current energy needs
Energy consumption
o Electrophysiological events require energy
o Amplitude of potential changes not necessarily best predictor of energy consumption
▪ Action potential
o Restoring resting potential requires energy → energy consumption of neuron could correlate with number of action potentials
o Pre- and post-synaptic factors (e.g., neurotransmitter release) also require energy
o Exact energy distribution to different processes can vary (species, neuron type)
Action potential
Passive chain of events that does not consume much energy
Maps in the brain - Clustering
Noninvasive methods cannot achieve single neuron resolution
▪ Methods with highest spatial resolution still average signal from many neurons.
Maps in the brain - Neurons of similar functional properties are clusrered together
o The more clustering, the more the averaged signal from many neurons corresponds to the signal of the individual neurons → sensitivity of a noninvasive imaging technique depends upon amount of clustering present
o Clustering on different spatial scales
▪ Topographic areas: for example the somatosensory homunculus but also for auditory or occipital information
Temporal resolution
The smallest unit of TIME that can be differentiated by a method
Spatial resolution
The smallest unit of SPACE which can be resolved
Invasiveness
majority of methods are either fully invasive (skull needs to be penetrated) or not invasive at all
o Invasive methods: used mostly in animal studies
o Non-invasive methods: also used for humans
Measuring brain structure
- Histology
- Structural magnetic resonance imaging (MRI)
Histology
o Cutting brain in pieces (e.g. slice of mouse brain)
o Process chemically for visualization of specific structure
▪ Makes us able to differentiate between the 6 brain layers, and between different structures in the brain
Structural magnetic resonance imaging (MRI)
o Investigation of anatomy in individuals
o Anatomical localization of functional findings
o Relate anatomical structure to differences between participants in e.g. behavior, disease classification
Measuring hemodynamics
- Changes in blood and tissue oxygenation, blood flow, and blood volume
- Temporal resolution of hemodynamic imaging is poorer compared to electrical imaging due to slowness of hemodynamic events
o hemodynamic events take 16 sec to develop - Spatial resolution varies strongly (but range smaller than for electrical signals):
o (invasive) optical imaging: columnar structure visible
o (non-invasive) fNIRS: several cm
NIRS -> PET -> fMRI
Measuring electrophysiological activity
- Spatial resolution
- Quiroga et al. (2005): single unit recordings in epilepsy patients
- Pitcher et al. (2011): EEG study
Spatial resolution, affected by
o Distance electrode and source of the signal
o Intermediate tissue (e.g. skull)
o Noninvasiveness: highest frequencies cannot be picked up
▪ Different frequency bands contain very different information!
Quiroga et al. (2005): single unit recordings in epilepsy patients
o Theory that in every person there is only on neuron that responses to a picture of their grandmother. For every different face a different neuron responds.
o Very exciting, but rare, ethical constraints, and difficult experimental control
→ less invasive techniques in humans
Pitcher et al. (2011): EEG study
o Signal of EEG-electrodes on back of the head, averaged across many trials of viewing faces (red) or chairs (blue)
o Amplitude of N170 & P1 is stronger for faces versus chairs
o Due to low spatial resolution of EEG these components do not differentiate between Aniston, Pitt, …, and anatomical localization is poor
Peripheral measures
Always good to measure peripheral data, in addition to the variables you want to measure
- Skin conductance
- Heart activity
- Muscle activity
- Eye measures
Skin conductance
o index of (sympathetic) arousal intensity in affective or cognitive processing
o highly variable, difference between subjects is huge
Heart activity
o heart rate
o heart rate variability: measures influence of PNS on heart
o blood pressure: measure of stress
Muscle activity
o Facial EMG (electromyography) as a tool for inferring affective states
Eye measures
o Eye movements: good measure of visual attention
▪ Saccades (fast movements of the eyes): Very fast (20-40 ms), no new information is acquired during saccades
▪ Fixations : Information acquisition occurs (mainly) during fixation
▪ Proudfoot et al. (2017) → Eye tracking in ALS patients
Trail making test A & B: connect the dots -> 1-2-3 / 1-A-2-B-3-C etc.
o Pupil dilation
▪ indicative of intense emotional arousal toward both pleasant and unpleasant stimuli and experiences
▪ Bradley et al. (2007): pupil dilation reflects SNS activity Pupil diameter larger for pleasant & unpleasant conditions than for neutral
