Seminar 3 Flashcards
Neuroimaging cannot teach us about causality
Observing neural activity with EEG, MEG, fMRI can only provide correlational evidence
- if we don this, we observe that physiological activity
Only way we will ever be able to collect evidence from healthy people
Observing neural activity cannot teach us whether a stimulus causes a given physiological activity
This is why studying only 1 brain damaged patient ill have more weight than 1000 healthy patients when it comes to brain localisation of function
Atypical or injured nervous system as a window into cognitive causality
Atypical or immured brains (or nervous systems) offer us a unique and extremely precious opportunity to study causal links in the cognitive system
We can lying physiological differences to differences in behaviour and reasonably assume that there is a causal connection between the physiological differences and behaviours
Brain lesions
(Insight into causal contribution of areas ton cognitive function (localisation))
Single most important way to study localisation of function
Individuals with (focal) brain lesions hep;p us to understand:
- the function contribution of individual brain areas to the cognitive system
- the functional connectivity of brain areas with one other
Brain lesions are categorised in relation to the cause of the lesion:
- trauma (e.g. accidents)
- stroke (e.go. Haemorrhaging, ischemic)
- surgical lesions (e.g. when cancerous tumours are removed, or intentionally removing brain areas in animal studies)
Single, double and triple dissociations
Single:
The loss or impairment of a brain function can be related to a single physical difference in the brain \
E.g. focal lesion as a result of a stroke
Double:
A situation in which a single dissociation can be demonstrated in one person and the opposite type of single dissociation cam be demonstrated for another person
E.g. Broca and wernicke’s patients
Triple:
A situation in which an single dissociation of related brain processes can be demonstrated in 3 different individuals indicating independence of subprocesses
Extremely rare - almost impossible;e to see naturally
Dissociations
Double dissociation - when taken into the context of each other, these 2 single dislocations form a double dissociation because they are both related to the same cognitive function (language)
Broca (1861) - single dissociation - p;a gauge production related to frontal lobe
Wernicke (1974) - single dissociation - language comprehension related to temporal lobe
Causes of brain damage
Stroke
Tumour
Trauma
Stroke
Strokes result in (sudden) focal lesions combined with sudden loss of function that helps us to understand brain-behaviour connections
Stroke lesions are the biggest type of lesion used in studies of localisation of fucntion
Ischemic stroke - a clot blocks blood flow to an area of the brain
Hemorrhagic stroke - belle ding occurs inside or around the brain tissue
Strokes follow blood vessel anatomy (spherically arteries) so you likely aren’t going ton have a stroke in one small area of the brain, but all the areas that specific artery supplies to (don’t follow brain anatomy) (4 man blood vessels in the brain)
Hemispatial neglect
A neuropsychological condition after brain damage (stroke) toy one hemisphere of the brain (motor and sensory cortex affected)
A deficit in attention to an awareness of one side of then field of vision/body, commonly contra lateral to the damaged hemisphere (left more often than right) N
Affects attention, perception, memory and movement
Typical symptoms:
- inability to process and perceive stimuli on one aide of the body or environment that is not due to lack of sensation
- a patient might fail to eat the hood on the left hand side of their plate, even though there complain of being hungry, only shave or apply makeup to the non-neglected side, bump into objects on neglected side, patients denies ownership of a limb or even an entire side of the body, eye-movements during dreaming ignore one side
Tumours
Tumour removal also results in (surgical) focal lesions when removed
Tumours take over neurotissue and it is dysfunction and expands by continuing to eat the tissue, pushing healthy issue to the side and making healthy tissue around it die
Compared to strokes, the lesion caused by a tumour grows slower, giving the brain time to relocate functions due to brain plasticity
While these lesions still help us understand brain-behaviour connections, the evidence is not as strong as with stroke lesions
This is because the rerouting of neural activity has occurred, so the locations of functions won’t be entirely representative of the general public
Lesioning techniques
Removing part of he brain either surgically or by injection of chemical substances that locally break down tissue
Used to treat neurological dysfunctions in humans (similar to tumour removal)
Used to test causal role of given brain areas in certain cognitive functions in animal studies
Trauma
Trauma to the head also results in brain injury
Different from stroke and tumour removals these injuries are not usually focal but concern large areas of the brain (to different degrees)
- hard to localise and quantify damage
Brain injury from trauma can also come with secondary stroke due to internal bleeding (hemorrhagic)
Coup and contrecoup injury:
- coup - primary impact - brain collides with the skull at the point of impact
- contrecoup - secondary impact - brain collides with skull opposite the point of impact due to the momentum caused by the first impact
Phineas gage: the first proof of localisation of function
I9n 1848, an incident changed our understanding of the relation between mind and brain
Phineas Gage a 25 year old railroad foreman had an accident where an explosive drove a tamping iron through his check and out of his skull
Despite his injuries, he remained conscious and only a few minutes later was sat up writing
After weeks of infection he seemed to recover
However, he did show severe personality changes
He became vulgar, childish, violent, friends and family did not recognise him
We now know that the areas of the basin that were injured in Gage’s case are responsible for rational decision making, short-term memory, motor attention, inhibitory control (especially impulse control), social cognition, sexual behaviour, emotion and affect
Founding case study of localisation of function
Neurodegenerative diseases
Neurodegenerative is the progressive loss of structure or function of neurones, which ultimately involves cell death and loss of brain tissue
Illnesses classified as neurodegenerative are a heterogenous group of disorders that are characterised by the progressive degeneration of structure and function to the central nervous system or peripheral nervous system
We can’t cure neurodegenerative disease (as we cannot regrow lost brain tissue), only delay progression which may be morally questionable in advanced stages
Aim of research is to improve early recognition and securely sloe down or even stop progression
Alzheimer’s disease and dementia
Alzheimer’s diseases is caused by abnormal buildup of proteins in and around brain cells resulting in loss of neurones and synapses
- amyloid forms plaques around brain cells - this coats and suffocates the brain, causing it to die
- tau forms tangles within brain cells - means neurones can’t fire, which leads to it losing its function
Alzheimer’s disease affects the cerebral cortex and certain subcortical structures, resulting in gross atrophy of the temporal lobe, parietal lobe and parts of the frontal cortex and cingulate Gyrus
Usually starts in temporal lobe and moves upwards
Behavioural profile of Alzheimer’s disease
Usually diagnosed when it is badly affecting the temporal lobe, as this is where the symptoms start to show - usually have already lost a lot of brain tissue, but but to the plasticity of the brain, it ha managed to compromise for the loss of brain tissue up to this point
Early symptom is difficulty in remembering recent events (forming new memories and storing them in the LTM, usually episodic)
As the disease advances, symptoms can include problems with language disorientation (easily getting sot), mood swings, loss of motivation, self-neglect and behaviour issues (e.g. aggression)
As a person’s condition declines, they often withdraw from family and society
Gradually, bodily functions are lost, ultimately leading to death
Singing into brain systems linked to:
- memory (episodic & knowledge structure)
- language (decay of mental lexicon)
- neural degeneration
- forgetting
- executive function
Because function is lost regularly and fgollows a typical pattern, we can have a big insight into brain localisation, specifically in the temporal a lobe as this is where I starts, suggesting this is where episodic memory is located (due to troubles with periodic memory being one of the main first symptoms)
Brains can look Ismaili in long term alcoholics
