2- Understanding brain-behaviour relationships Flashcards
Give gross anatomy of brain
Cerebrum= left and right hemispheres separated by longitudinal fissure, connected by corpus callosum. 4 lobes in each hemisphere. Cortex and subcortex.
Cerebellum= flocculonodular, anterior and posterior lobes
Brainstem= pons, medulla, bulbar
Where/What is Brocas area?
Left inferior frontal gyrus. BA44/45
Comprises 2 separate substructures: pars opercularis, pars triangularis.
Language production and some comprehension, verbal working memory
Where is Wernicke’s area?
Posterior section of the SUPERIOR TEMPORAL GYRUS. BA 22.
Connected to Brocas area by the arcuate fasciculus.
Where/what is the basal ganglia?
Subcortex- caudate, putamen, globus pallidus, substantia nigra, subthalamic nucleus.
Involved in movement, planning and cognition. Impacted in Parkinson’s disease.
Start, stop, regulate intensity of voluntary movements.
What is behaviour?
Behaviour is psychological. Mental construct based on your interpretation of what you sense. Includes memory, language, attention, emotion, visuospatial, executive functions, cognitive-motor functions.
Dissociations of behaviour: What is single dissociation?
Two groups differ in one task (behaviour); one group has a specific lesion the other one does not (neurotypical controls)
Example- a group of people with damage to Wernicke’s area has poor spoken comprehension, compared to healthy controls.
Inference- therefore Wernicke’s area is responsible for spoken language comprehension.
What is double dissociation of behaviour?
Two groups of persons with different brain lesions show different behaviours on two different tasks
A group of persons with damage to Wernicke’s area has poor language comprehension but fluent language.
A group of persons with damage to Broca’s area has relatively good language comprehension but non-fluent language
Inference/conclusion: Therefore, Wernicke’s area is responsible for spoken language comprehension.
Double dissociations provide stronger evidence in comparison to single dissociations.
Converging evidence in the study of brain-behaviour relations
CONVERGING EVIDENCE= similar conclusions from multiple research methodologies and populations, including animal brains.
What are the broad theoretical traditions in investigating brain-behaviour relationships?
- Localisationist
- Equipotentialist
- Dynamic localisationalist
What is the belief of localisationists?
Separate, discrete functions can be narrowly related to separate discrete locations in the brain.
If you know the site of the lesion or the behaviour you can predict one from the other.
What is the belief of equipotentialists?
Opposite from localisations- precise mapping of behaviours is impossible.
Localisation for ‘lower’ order control or sensory input e.g. primary motor cortext, but higher functions involve the WHOLE CORTEX
Impairment due to generalised change, not damage due to a specific area
Language, perception, memory etc. are unitary not fractionated functions.
If subparts appear differentially affected, this is due to:
Peripheral disruptions of in/output
Effects of internal organisation
What is the belief of dynamic localisationists (or interactionists)?
Combined actions of multiple brain areas allow higher functions (language, praxis, perception)
There is specialisation for different parts of the brain, BUT functions only occur through coordination and interaction of all these specialised parts
1) Interaction, interdependence
2) Behaviours emerge from this network
3) Adaptability, plasticity- can arrive at solutions via several routes, combinations
Neuroimaging methods are split up into…
Anatomical- “where; still pictures”
Functional- “when & where” neural activity in brain is associated with the ability to perform a particular task. DYNAMIC
Anatomical methods: Brain autopsy
Old but still valuable today. Currently the only way to make a definitive diagnosis in some diseases, for example dementia.
Anatomical methods, structural neuroimaging techniques. MRI
Magnetic Resonance Imaging (MRI)
Uses strong magnetic fields to “magnetise” different atomic modules in brain tissues thus generating picture contracts. Enables naked eye to distinguish grey from white matter.
Anatomical methods, structural neuroimaging techniques. CT
Computer Tomography (CT) or Computer Axial Tomography (CAT)
Earliest technique, now largely replaced by MRI
Uses radiation to produce images.
Functional Neuroimaging methods- EEG
EEG= electroencephalography
Directly measures electrical activity associated with neural firing.
Neurons produce electrical activity which is recorded from electrodes on skull. Real-time measurements of brain activity.
Difference in voltage between electrode pairs measured. It measures the brain’s electrical activity as a whole, capturing neural oscillations over time.
Detects changes that happen in a few milliseconds (high temporal resolution).
Global EEG- measures neural activity during different brain states such as sleeping and waking,
Event-related potentials- EEG activity averaged over a series of trails triggered by the same event (e.g., the presentation of a visual stimulus)
Compare and contrast EEG with MEG
Both DIRECTLY measure neuronal activity.
Magnetoencephalography is newer. While EEG measures electrical activity associated with neuronal depolarization, MEG records the magnetic field produced by this electrical activity.
Both primarily from the activity of PYRAMIDAL NEURONS.
MEG records activity oriented parallel to brain’s surface so records cells in superficial sulci, therefore more limited in its scope.
EEG records activity oriented perpendicular to brain’s surface so records cells in depths of sulci.
Advantage of MEG over EEG is that signal is less sensitive to head-shape, less signal distortion.
Functional method- fMRI
Functional Magnetic Resonance Imaging
Indirectly measures neuronal activity, operating under principle that neural activity is supported by increased blood flow. Most widely used brain imaging technique.
Changes in blood flow (haemodynamic) and levels of oxygen within the blood are linked to neuronal activity.
fMRI can show changes in the brain that result from different experimental conditions, computer combines many images taken less than a second apart. However EEG has better temporal resolution.
Physiological changes: More blood flow results in more glucose and more oxygen (haemoglobin). When processing going on, more blood supply.
Haemoglobin differs as to how it reacts to magnetic field (contains iron)
Physiological changes are localised within 2-3 mm in brain region.
Person is tested in the scanner, with a baseline condition and another condition–> importance of choice of subtraction tasks in levels of brain activation.
What are the advantages of fMRI?
Wide-spread availability of MRI scanners, relatively low cost per scan, good spatial resolution, better temporal resolution than other INDIRECT methods.
Functional method- PET
Indirectly measures neuronal activity
Positron Emission Tomography. Measures blood flow to neurones. Small amount of radioactive tracer injected, tracer enters brain and in following 30s radiation of brain rises to its maximal value, picture taken.
Advantage over fMRI is choice of tracer.
Disadvantage= cost, poor temporal resolution, 1 min compared to 6-8s for fMRI, PET more invasive than fMRI so not suitable for children.
Functional method- NIRS
Near-infrared spectroscopy. Indirectly measures neuronal activity.
Changes in haemoglobin concentration affect absorption of infrared light. NIRS non-invasive, compared to optical imaging in animals, Cortical surface not exposed in NIRS, light scattering by skull leads to reduced spatial resolution.
+ EROS (event-related optical signal) Not as sensitive to head movements as fMRI, more promise for study of children.
Trade-Offs between Temporal and Spatial Resolution
Direct functional methods of neural activity e.g. EEG and MEG have exquisite temporal resolution, sensitive to changes on a millisecond. BUT poor spatial resolution so difficult to pinpoint the precise origin of the signal.
Indirect methods e.g. fMRI have better spatial resolution than EEG/MEG but poorer temporal resolution.
Localisation vs Association
We can say X area of the brain lights up when we do Y
Not:
X area is responsible for Y
But maybe, X function is ASOCIATED with Y area.
Remember neural activity often indicates inhibition of function as well as its activation
Functional neuroimaging- ERP (a variant of EEG)
ERP= Event-related Potentials are very small voltages generated by brain structures in response to specific events or stimuli. ERP is made up of many positive and negative waves.
Rather than measuring the brains neural activity as a whole (EEG) it examines brains responses time-locked to specific sensory, cognitive, motor events eg. visual stimulus, sound etc.
Timescale of a few hundred milliseconds
Waves are numbered according to time at which they are produced or their order of occurrence
Compare/Contrast Electrophysiological vs haemodynamic methods
Electrophysiological methods measure neural activity directly
Haemodynamic methods give indirect measure of neuronal activity
Areas where the brain is most active make the greatest energy demands –> increased blood flow in these areas
What are the problems of neuroimaging
Limited availability of neurophschological patients - patients with specific brain lesions.
Considerable variability between individuals- problems when images averaged across individuals
Unlike lesion techniques, cannot demonstrate necessity of a brain region for a specific cognitive process.
Level of resolution of images (temporal, spatial, variability from scanner to scanner)
Other problems- heavily processed data in terms of statistics, artefacts (muscle movement in ERP)
Benefits of neuroimaging techniques
Can demonstrate that humans without neurologic damage routinely recruit a specific region to perform a task.
Can compare levels of activation across individuals and between trials. Functional brain imaging can characterize a region’s contribution to a cognitive process.
Hemispheric Asymmetry
The frontal lobe is larger in the right hemisphere
The Occipital lobe is larger in the left hemisphere
Examples of lateralized functions in the left hemisphere
Language- Broca’s area (BA 44 & 45) but some right-handed person may have language in RH.
Herschl’s gyrus (BA 41) is more dense on the left than the right hemisphere.
Right ear advantage reflecting left hemisphere language dominance.
Examples of lateralized functions in the right hemisphere
Prosodic aspects of linguistic processing
Visuospatial processing
Facial processing and social expressions (fusiform gyrus)
Emotional processing
Frontal lobes is split up into different cortices.. what is the function of primary motor cortex
Voluntary movement control
Speech (lips, tongue)
Spelling
Chewing
Swallowing (voluntary aspect)
Frontal lobes is split up into different cortices.. what is the function of premotor cortex
Selection of movements/planning of movements
Frontal lobes is split up into different cortices.. what is the function of orbital cortex
Personality
Social Behaviour
What is the function of the prefrontal cortex?
Programming of sequences of behaviour
Problem solving
Decision making
Voluntary eye movements
Judgement
Memory and attention
Personality
Social behaviour
The temporal lobes are split up into different areas.. what is the function of PRIMARY AUDITORY CORTEX (Heschl’s gyrus)
Reception of auditory stimulation
Perception of auditory stimuli (superior temporal gyrus)
Auditory cognition
The temporal lobes are split up into different areas.. what is the function of Wernicke’s area (BA 22)
Left superior temporal gyrus
Language understanding
The temporal lobes are split up into different areas.. what is the function of HIPPOCAMPUS
Hippocampus is in the medial temporal lobe
Left= verbal memory
Right= spatial memory
The temporal lobes are split up into different areas.. what is the function of the RIGHT TEMPORAL LOBE
Face perception (fusiform gyrus)
Musical abilities
The parietal lobes are split up into different areas.. what is the function of the SOMATOSENSORY CORTEX
Sensation from opposite side of the body Spatial discrimination
Perception (body, tactile, visual)
Stereognosis (tactile perception and recognition)
Kinaesthetic feedback (clumsy movements)
What is the function of the right parietal lobe?
Spatial (or visuospatial) orientation and attention- visuospatial neglect typically arises after right hemisphere parietal lobe damage.
What is the function of the occipital lobe?
Visual sensation- points of light, simple forms
Visual perception- contours, orientation, depth, colour, stereopsis, brightness, movement.
Semantic connotation of objects
Reading
Function of the cerebellum
Coordinates muscular activity so it is not jerky
Posture
Locomotor mechanism (movement, co-ordination, balance)
Ataxia: disorder of movement
Ataxic dysarthria: “scanning” speech, aprosodic/ no prosody (robotic, monotone)
Friedich’s ataxia
Spinocerebellar
Broader cognition- perception, lang, working memory, cognitive control.
