KNOW THESE BETTER PT. 2 Flashcards
NEUROIMAGING
Why Structural neuroimaging?
- clinically important to guide interventions
- scientifically important to link injuries/dysfunction to outcomes
Cerebral aniography - Used to locate:
Used to locate:
- vascular damage
- large tumours
- Arteriosclerosis
- aneurisms
Computed tomography (CT)
- Also a version of x-ray scanning
- Rotates x-ray source and detector to reconstruct image based on density of tissue (fat vs tissue vs bone)
Computed tomography (CT) - USED FOR:
skull fracture, intracranial bleeds, tumours
CT is only as good as its algorithms - PROS/CONS:
- Pros: quick, inexpensive
- Cons: radiation exposure (after multiple)
MRI - PROS/CONS
- Pros: spatial resolution
- Cons: slow and expensive; excludes patients with pacemakers, metal
Variant of MRI:
Diffusion Tensor Imaging (DTI)
- Variant of MRI
- Relies on how water molecules move in the brain
- Pros: good for network connectivity & white matter
- Cons: expensive; computationally complex
Functional Neuroimaging - 3 potential applications
- studying mental states without requiring a response e.g., mind-wandering, lying
- understanding mechanisms of brain dysfunction
- understanding altered states of consciousness
Functional Neuroimaging - TYPES:
- Electroencephalography (EEG)
- Positron Emission Tomography (PET)
- Functional MRI (fMRI)
Electroencephalography (EEG) - USE
- Electrodes on scalp surface detect electrical activity in cerebral cortex
- Used for: epilepsy, delirium, encephalitis
EEG: PROS/CONS
- Pros: quick, inexpensive, high temporal resolution
- Cons: hard to measure deep brain structures, low spatial resolution
PET scan
- Positron Emission Tomography (PET)
- A radioactively labelled substance is injected and imaged
- e.g., active brain areas consume more fuel > show more radioactivity when a glucose-like molecule is injected
- Can also follow metabolism of radiolabelled drugs
PET - use, PROS/CONS
- Less common with rise of fMRI
- Pros: useful for looking at specific systems (e.g., DA) or proteins (tau); useful for looking at lifespan/condition changes (e.g., stroke, CTE)
- Cons: expensive, poor spatial resolution
fMRI: Paired image subtraction
A) Task of interest: remembering learned words
* Cued recall
B) Stuff we want to control out: Motor components of speech, Visually reading something on-screen, hearing loud MRI sounds, etc.
* Baseline
6 fMRI Challenges
- Spatial averaging: Over trials & over subjects > can produce epiphenomena
- Temporal resolution: Blood changes slower than electrical activity; May miss brief but important events
- Doesn’t tell us about causality
- Focus on increases in activity - Important but tonic activity would be subtracted out
- Testing environment - Need to make many pipeline choices > correcting for different anatomy, filtering noise, correcting for multiple comparisons, etc.
- Replicability and statistic flexibility - Some regions are more active during “rest” than during goal-oriented tasks:
> medial prefrontal cortex, posterior cingulate cortex, angular gyrus/lateral parietal cortex
May be for inwardly-focused attentional processes; construction of the “sense of self”
RECOVERY FACTORS:
Consequences of anosognosia
- Low engagement with rehab
- Medication non-compliance
- Poorer treatment outcomes
- Poorer use of compensatory strategies
- Stress and isolation for both affected person and their care partners
- Need for more supervised or structured living arrangements
Methods of diagnosis for Anosognosia
- Clinician judgment (structured interview e.g., Self-Awareness of Deficits Interview)
- Patient-care partner discrepancy (questionnaires e.g., Awareness Questionnaire)
- Self-appraisal performance discrepancy (variety of cognition & memory measures)
Neurological correlations with anosognosia
- reduced metabolism
- cell density
- blood flow in a set of frontal, cingulate, and medial temporal regions associated with cognitive processing of self and the default mode network
Anosognosia Treatment
Some intellectual awareness necessary to start
Usually through occupational therapy
Multimodal training with feedback:
- Real-life settings
- Guided experience
- Multimodal feedback
- Dialogue between therapist and patient
Recovery from injury across age
- Damage to a given brain area at different times in life leads to very different outcomes
- Margaret Kennard (1899-1975) showed that the impact of motor cortex damage was age-dependent
Age-dependent recovery
Across age, brains change in their: (Giza et al., 2009)
- Receptor expression
- Level of synaptic pruning
- Level of neurite (axon/dendrite) outgrowth
- Blood flow
- Metabolic patterns
- Myelination
- …
All of these factors shape responsiveness to injury (good & bad)
Impact of lesion size on recovery
- Larger lesions tend to result in greater functional impairments
- Bilateral lesions show less recovery than unilateral - don’t have that counterpart area on the other side of the brain that could lessen the load
Chronic vs acute dysfunction
- Massive slow-growing tumour > little impairment
- VERSUS
- Sudden stroke with associated damage of comparable size > functionally devastating
For humans, what are the benefits of an enriched environment in brain injury recovery?
FROM ENRICHED ENVIRONMENT STROKE STUDY:
- activity levels increased (sustained after discharge)
- length of stay shorter
- modified Rankin scale (6-point measure of functional independence) not different at discharge
Secondary effects of injury - edema
Edema – following stroke or brain injury, there may be considerable swelling
Secondary effects of injury - blood flow
- Blood flow – locally changes following injury
- These can be temporary
Secondary effects of injury - Diaschisis
Diaschisis (“shocked throughout”) – sudden change of function (metabolic depression) in a portion of the brain connected to a distant, damaged area
Post-injury improvements (3)
- Dissipation of secondary effects
- Compensation
- Plasticity
ATTENTION
Recovery can include…
- Allesthesia
- Simultaneous extinction
- Spectrum of recovery
- Prismatic adaptation
Allesthesia
- Responding to stimuli on the neglected side as though they were on the non-neglected side
- Mislocating the stimulus (someone touching their left hand, allesthesia - able to detect that they are touched, but on their right hand)
Simultaneous Extinction
- Responding to stimuli on the neglected side unless both sides are stimulated simultaneously, then they only notice the ipsilateral stimulus
- The easily detected stimulus “extinguishes” detection of the other stimulus
Balint’s syndrome
- A severe disruption of attention based on a large region of brain damage
- Bilateral damage to parieto-occipital lobes (stroke, some dementias, some trauma)
- Primary sensory processing, language, memory and judgment intact
3 functions of Balint’s syndrome
- Oculomotor apraxia
- Optic ataxia
- Simultanagnosia
Peripersonal space
- The space around our bodies is prioritized by the attention system = “peripersonal space” (PPS)
- Within PPS, line bisection performance is biased leftward, outside it is biased rightward
- A larger PPS is correlated with trait anxiety and claustrophobia
- A smaller PPS is correlated with autism and schizophrenia
MEMORY
watch the video
Researchers believe that the process of consolidation is mediated by…
The hippocampus
…and that individual memories are stored diffusely throughout the cerebral cortex
Sleep is important for this!
The memory qualitatively changes - is this still the “same memory”?
Memory dysfunction: Korsakoff Syndrome
- Result of brain damage due to thiamine (vitamin B1) deficiency
- Often (but not always) due to heavy alcohol consumption
- Often (but not always) preceded by Wernicke’s encephalopathy – an acute brain reaction to lack of thiamine: confusion, abnormal eye movements, hypothermia, coordination problems, coma
Korsakoff Syndrome - types of amnesia
Severe anterograde amnesia, mild retrograde amnesia – limited to explicit memory
Often confabulate – report inaccurate stories about event (never say “I don’t know”)
Korsakoff Syndrome - damaged structures
medial diencephalic structures (thalamus & hypothalamus)
diffuse damage to cortex, hippocampus, cerebellum
Korsakoff Syndrome - treatment
thiamine supplements + nutrition
address alcohol use if relevant
SPLIT-BRAIN
Agenesis of the corpus callosum vs. adult split brain patients
- Language skills, IQ fairly normal (unless other abnormalities present)
- Surprisingly minimal “disconnection syndrome” compared to adult split-brain patients!
- Plasticity in children allows alternative cross-hemispheric pathways (e.g., anterior commissure) to be reinforced
- If the task requires very complex integration of information across hemispheres (e.g., compare visually complex shapes across the midline, fast) some impairment is seen
DYSFUNCTION OF PERCEPTION
do other brainscape
Sensorimotor Dysfunction
*do other brainscape
