Summary Cognitive Neuropscyhology (blue = book and Q&A session
incorporated)
Week 1 – Lecture 1 – Introduction
Cognitive Neuropsychology
Definition
= The study of the relation between structure and function of the brain and specific cognitive
functions (e.g. language, memory, attention, ...)
- 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)/lesions
- First only this was done
Brain enthusiasm
Scientific potential vs science fiction
- Claim by Verbeke (2009): in 5 years, brain scans will be common when applying for
important jobs
- Brain scan can tell us whether someone is good fit for the job and whether their
behaviour is good or detrimental (= schadelijk) for the position
- 2020: brain scans are still not standard practice
- Not reliable to state about a single person
- Need more data, a group
- Brain scans as evidence in court of law
- Personality assessment
- Control of actions
- "Don't blame me, blame my brain."
- Lie detection
- Brain scans might be overinterpreted by laypersons
- (more than =) > expert witness
- Because of persuasive power of “neuro-”
- Brain scan provides just as much information as psychiatrist (expert witness)
- Brain imaging can be used to test the state of consciousness of patients in vegetative state or
locked-in syndrome
Persuasive power of “neuro-”
- Ali et al. (2014): How much are individuals ready to believe when encountering improbable
information through the guise of neuroscience?
- Students could easily be convinced that fake neuroimaging instrument (salon hair dryer)
could predict/read their thoughts
- Students deemed technique highly plausible and were hardly skeptical
Objective diagnosis of diseases?
- Good progress for several neurological syndromes
- Brain tumors, dementia, mild cognitive impairment, ...
- But less progress for psychiatric and mental syndromes
- Depression, autism spectrum disorder, schizophrenia, ...
1
, - Differences on a group level
- But not large and consistent enough to allow diagnosis of an individual subject
Basis of neural signals
- Neurons, with cell bodies in grey matter of cerebral cortex and subcortical structures;
white matter contains long axons
- Action potential travels along the axon to all terminals (synapse)
- Action potential is generated at a difference of 55 mV
- Neurons provide excitatory (more active; e.g. glutamate) or inhibitory signals (less active;
e.g. GABA)
- Without input (at rest), cell membrane of a neuron has an electrical potential difference
between in- and outside of -70 mV (= micro Volt)
- Resting potential
- Post-synaptic potential is determined by integrating input of many synapses at the dendrites.
It can hyper- and depolarize
Neural communication
- Input neurons (through neurotransmitters): action potentials over time
- Membrane potential of post-synaptic neuron depolarizes (less negative: -70 mV
→ -65) or hyperpolarizes (more negative: -70 → -73)
- Over time, membrane potential of post-synaptic neuron changes in function of input it
receives
= Signal
- Summary of level of input, relative degree excitatory/inhibitory input, when action
potential is triggered
- Schematic potential at axon hillock
- Potential difference reaches a critical level → further decrease of potential difference →
overshoot so that the difference becomes positive → very quick restoration of a negative
difference
= Action potential
Signal description
- Simplest signal = sinusoidal oscillation of just one frequency, for example a pure tone
- Frequency: rate of change of signal, e.g. in the time or space dimension
- 1 Hz = completing a full cycle (going up & down) in one second
- 2 seconds for 0,5 Hz (whole signal) & 4 seconds for 0,25 Hz
- Biological signals never contain just one frequency (happens in artificial signals, e.g.
pure tone)
- 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 (how often the signal is measured)
2
, - 1⁄2 * 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 = no high frequencies (weakened or completely removed)
- Smoothing
- High-pass = no low frequencies
- Band-pass = particular phase
- Spectogram: strength of each signal component at each moment in time
- Often displayed by a colored diagram
- X-as: time & Y-as: frequency
- Zero strength/amplitude = blue & highest amplitude = red
- Patch clamping: sucking part of membrane with the tip of a pipette and then measuring the
membrane potential
- Highly invasive
- Requires very stable substrate
- Not used in human research
Molecular and hemodynamic signals
- 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+ (= sodium/natrium), repolarization: outward
current/efflux of K+ (= potassium/kalium)
- E.g. calcium concentration high in electrically active neurons → two-photon calcium
imaging
- Calcium is involved in processes such as neurotransmitter release, plasticity
and gene transcription
- At a larger scale: hemodynamics (= blood)
- Blood supply is adjusted to current energy needs and changes over time
Energy consumption
- Electrophysiological events require energy
- Amplitude of potential changes not necessarily best predictor of energy consumption
- Action potential = passive chain of events that does not consume much energy
- Restoring resting potential (afterwards) requires energy → energy consumption of neuron
could correlate with number of action potentials
- Pre- and post-synaptic factors (e.g., neurotransmitter release: presynaptic, functioning of
postsynaptic receptors, maintenance of resting potential in the absence of any action
potentials or synaptic input) also require energy
- Exact energy distribution to different processes can vary (species, neuron type)
- When region receives a lot of inhibitory input → many presynaptic terminals that release
neurotransmitter that inhibits the postsynaptic neurons → very little action potentials fired →
percentage of energy consumption related to presynaptic functioning might be higher overall
3
, Maps in the brain
Clustering
- Noninvasive methods cannot achieve single neuron resolution
- Methods with highest spatial resolution still average signal from many neurons
- Neurons of similar functional properties are clustered together
- Clustering = the tendency of neurons with similar functional properties to be
physically nearby
- 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
- Clustering on different spatial scales
- At different levels of the brain
- Columnar organization in many brain regions
- Column = cylinder-like volume in the cortex that runs through all cortical layers all
the way from the surface of the brain to where gray matter is bordered by white matter
- Cortical thickness: 2-4 mm
- Neurons
- Within column, neurons have very similar response properties
- Topographical: part of body (arm) clustered in same place in brain
- Area: a particular region has a specific function in the cortex
- Middle temporal (MT) area: neurons show a strong selectivity for the direction of
motion of a visual stimulus
- At largest scale, areas show a preferential connectivity and overlap in functional
properties with other areas (usually areas that have a close proximity)
- Areas form cortical structures
Illustration
- Orientation columns (containing neurons with similar preference for line orientation):
not in all species
- Imaging at 20 μm (= micrometers) resolution (invasive optical imaging): orientation
columns visible
- Imaging at lower resolution: blurred, no location would contain the strong selectivity as is
actually present at the level of the single columns
Overview of methods
- Three dimensions:
1. Temporal resolution: the smallest unit of time that can be differentiated by a method
- Resolution of ms is needed to measure individual action potentials
2. Spatial resolution: the smallest unit of space which can be resolved
- Which scale of organization can be picked up
- High = single-neuron
3. Invasiveness: majority of methods are either fully invasive (skull needs to be
penetrated) or not invasive at all
- Focus on less invasive techniques (=> can be applied in humans)
- No methods available that have high spatial resolution combined with high temporal
resolution
4
