Neuropsychology: The Lesioned and Stimulated Brain Flashcards
Why do we study the lesioned brain?
-Lesioned brain leads to particular deficits, behavioral problems, etc., so studying tells something about normal architecture of cognition and human brain (ex.: alien hand syndrome)
-Classical cases
-Taxonomy of brain manipulation methods
What is Alien Hand Syndrome?
-Syndrome characterized by involuntary movement typically of hand
-No control: movements occur despite what patient reports verbally to intention
-Result of brain damage
What is reverse engineering?
-Inferring function of brain region (or cognitive mechanism) by removing it and measuring effect on rest of system
-Disruption of brain can come from different causes: natural damage (stroke, trauma), elicited damage (animal models) or virtual damage (harmless temporary changes induced electro-magnetically (TMS))
Why are classical cases important?
-Able to infer function of certain regions
-Able to know how normal function works
-Reverse engineering
What different taxonomies are there of brain manipulation methods?
-First: distinction between non-invasive brain stimulation methods and other methods
-Second: more refined taxonomy where each of different causes divided into subcategories
What does the taxonomy of brain manipulation methods look like with the first method?
Distinction between non-invasive brain stimulation methods and other methods
-Non-invasive brain stimulation methods: tFUS, rTMS, tDCS, tRNS, tACS, single-pulse TMS
-Other methods: lesion, drug manipulation, local pharmacological inactivation, opto-genetics, micro-stimulation
What does the taxonomy of brain manipulation methods look like with the second method?
More refined taxonomy where each of different causes divided into subcategories
-Natural damage
–>Neurosurgery
–>Strokes: ischemic infarction or hemorrhage
–>Traumatic brain injury: closed or open
–>Tumor
–>Viral infection
–>Neurodegenerative disease: Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia, etc.
-Virtual (temporary) damage
–>TMS
–>tES
-Elicited damage
–>Aspiration
–>Transection
–>Neurochemical lesions
–>Reversible lesions
What different causes of natural brain damage are there?
-Neurosurgery
-Stroke
-Traumatic brain injury
-Intracranial tumors
-Viral infections
-Neurodegenerative disorders
What are characteristics of neurosurgery as a cause of natural brain damage?
-Performed to remove focus of epileptic seizures
-Side effects
–>Removal of medial temporal lobe: permanent brain damage and memory problems
–>Split brain surgery (cutting of corpus callusom): brain networks affected (can’t communicate anymore)
What are characteristics of a stroke as a cause of natural brain damage?
-Stroke: accident in arteries of brain, typically happens unexpected, but age is risk factor
-2 types: ischemic infarction and hemorrhage/bleeding
-Important to distinct types when person is having stroke: medication used in ischemic infarction cause damage in person with hemorrhage
–>Distinction by CT-scan
What is an ischemic infarction?
-80% of strokes
-Neurons in brain don’t receive blood due to plaques or cloths
-Motor and cognitive problems depending on location and size of affected area
-Some arteries more vulnerable to infarction
What is a hemorrhage/bleeding?
-20% of strokes
-Weak spot in blood vessel causes rupture
-Bleeding inside brain tissue
-People with aneurysm suffer more likely from hemorrhage
What are characteristics of traumatic brain injury as a cause of natural brain damage?
-Injury caused by external force
-Clinically diverse picture: broad range of cognitive, emotional and behavioral disorders, outcome from complete recovery to death
-Risk factors
–>Age: 0-4, 15-19 and 75+
–>Sex: more likely in males
-Causes vary: traffic accidents, fall from height, violence, etc.
-Mechanical forces can result in: open or closed TBI
-Seen in MR-scan
What is an open traumatic brain injury?
-Less common type of TBI
-When objects or bone fragments penetrate meninges
-More localized effects
-Can lead to infections
What is a closed traumatic brain injury?
-More common type of TBI
-When axons get damages: diffuse axonal injury
-More widespread effects
What are characteristics of intracranial tumors as a cause of natural brain damage?
-Tumor: mass of new tissue that persists and grows independently
-Origin
–>Meninges: meningioma
–>Glial cells: glioblastoma
-Classification in different ways
In which ways are intracranial tumors classified?
-Benign (low-grade tumors) vs malign (high-grade tumors)
–>Benign evolve into malign without removal
-Encapsulated vs infiltrating
–>Encapsulated: distinct entity that puts pressure on brain
–>Infiltrating: tumor not separated from surrounding tissue
-Primary vs secondary
–>Primary: originate from brain tissue
–>Secondary: originate elsewhere in body as metastasis of primary tumor
What are characteristics of viral infections as a cause of natural brain damage?
-Viral infection: invasion of body by disease-producing microorganism and subsequent tissue reactions
-Infections can kill neurons
In what ways can infections kill neurons?
-Interference with blood supply
-Interference with glucose or oxygen metabolism
-Alter cell membranes
-Form pus
-Cause edema
What are characteristics of neurodegenerative disorders as a cause of natural brain damage?
-Neurodegenerative disorders: increasing impairments in one or more cognitive functions
-Different types: Alzheimer’s disease, frontotemporal dementia (Pick’s disease), Huntington’s disease, multi-infarct (vascular) dementia, Parkinson’s disease
What is Alzheimer’s disease?
-Reduced grey matter
-Deeper sulci
-Increase of cerebrospinal fluid
-Large ventricles
-Neurodegenerative disorder that causes brain damage
What is frontotemporal dementia or Pick’s disease?
-Reduced grey matter
-Wider/deeper sulci
-Large ventricles
-Neurodegenerative disorder that causes brain damage
What is Huntington’s disease?
Neurodegenerative disorder that causes brain damage
What is multi-infarct (vascular) dementia?
-More white matter damage
-Information-processing problems
-Neurodegenerative disorder that causes brain damage
What are dissociations in neuropsychology?
-Dissociation: inferring something about cognition or brain by studying pattern of deficits in patients
-2 types: single dissociation or double dissociation
-Example: writing vowels vs consonants (Cubelli, 1991; Kay & Hanley, 1994)
What were the findings of the researches of Cubelli (1991) and Kay & Hanley (1994) about writing vowels vs consonants (dissociations)?
-Cubelli: observed patient who can’t write vowels, but can write consonants
-Hay & Hanley: observed patient who can’t write consonants, but can write vowels
-Writing vowels and writing consonants are independent things
-Inference that there are separate neural resources in brain for writing vowels and writing consonants
-Can lie in same location/brain area, but have different intermixed neurons
What are single dissociations in neuropsychology?
-Being impaired on task A but (relatively) spared on task B
–>Classical or strong dissociation
–>Example: patient with apraxia
-Inferences can be made from single dissociation
What is classical dissociation?
-Single dissociation
-Patient is impaired on task A, but performs normal on task B
What is strong dissociation?
-Single dissociation
-Patient is impaired on task A and B, but more impaired on one of the two tasks
-Both tasks use different cognitive functions and different neural resources
What is apraxia?
-Able to grab objects when asked
-Not able to mimic use of objects when asked
-Suggests that grabbing and pantomiming use different cognitive functions and different neural resources
What types of inferences can be made from single dissociations?
-Task A and B rely on different cognitive processes and/or different neural resources
-Task-demand artifact: suboptimal performance, misunderstanding
-Task-resource artifact: same resource, but more needed for task A
What are double double dissocations in neuropsychology?
-Two or more single cases with complementary profiles or strengths and weaknesses (example of vowels and consonants)
-Used to infer that 2 tasks/stimuli are separate neural and cognitive resources
What are associations in neuropsychology?
-Association of symptoms: being impaired on task A and task B
–>Perhaps functions are close together in brain?
-Syndromes: cluster of different associated symptoms
What are the 2 traditions of human neuropsychology?
-Cognitive neuropsychological approach
-Classical neuropsychological approach
What are characteristics of the cognitive neuropsychological approach of human neuropsychology?
-Can particular function be spared/impaired relative to other cognitive functions
–>Addresses questions of what building blocks of cognition are
–>Using single case methodology to answer question
-Associated with single dissociation
What are characteristics of the classical neuropsychological approach of human neuropsychology?
-What functions disrupted by damage to region X
–>Addresses questions of functional specialization, converging evidence to functional imaging
–>Using group study methods to answer question
-Associated with double dissociation
What are the different assumptions underlying single-case studies?
-Fractionation assumption
-Transparency assumption
-Universality assumption
What is the fractionation assumption?
Damage to brain can selectively impair cognitive function
What is the transparency assumption?
Other cognitive functions operate at normal pre-injury levels of efficiency
-Criticism, because of plasticity in brain
What is the universality assumption?
-All individuals share same cognitive systems
-Criticism, because inter-individual differences may skew data
Why would you use single-case studies instead of group studies?
-Researcher gets observations with individual differences when doing group studies
-Because every lesion is unique, it’s best not to cross-average across patients
-Evidence against group studies
-Use single-case methodology if you want to make inferences about the cognitive system
What are characteristics of group-studies?
-Different ways of grouping patients
-Complications
-Useful if you want to make inferences about lesion-deficit associations
What different ways are there to group patients in group-studies?
-Grouping by syndrome
-Grouping by behavioral symptoms
-Grouping by lesion location
What are characteristics of grouping by syndrome and what is an example?
-Useful for investigating neural correlates of disease pathology
-Not useful for dissecting cognitive theory (inferences about building blocks of cognition)
-Example: lesion neuroanatomy of posterior cortical atrophy (PCA) in which patients were grouped by syndrome (PCA) to scan and assess at group levels which brain areas affected by atrophy
What is posterior cortical atrophy (PCA)?
-Specific type of Alzheimer’s disease
-Dominated by perceptional problems rather than memory problems
-Degeneration of neurons mainly in posterior part of brain: occipital cortex, parietal cortex and bit in temporal cortex
What are characteristics of grouping by behavioral symptoms and what is an example?
-Useful for identifying multiple regions implicated in behavior
-Example: lesion in neuroanatomy of set-switching accuracy in which comparing patients with and without deficits to find lesion distribution in patients with deficit, patients grouped by behavioral symptom (deficit vs no deficit)
What are characteristics of grouping by lesion location and what is an example?
-Useful for testing predictions derived from functional imaging
-Example: contribution of parietal lobule to spatial attention in which patients were grouped by lesion location and found that patients with lesion surrounding temporal-parietal junction were impaired when stimuli occurred in contralesional visual field
What are the independent variables and dependent measures for the different types of grouping?
-Grouping patients by syndrome or symptom (IV): looking at lesion location (DM)
-Grouping patients by lesion location (IV): looking at symptoms (DM)
What are issues related to patient grouping?
-Some forms of brain damage make it hard to localize lesion
-Diaschisis: brain damage can induce functional lesions at distance (when regions function as network
-Dangerous to conclude that function is localized in region and that purpose of region is to support that function (neophrenology)
-Has to be considered whether region performs other functions or if other regions support this function
What summary can you give about single- or group studies?
-Single case studies: important to determine what components of cognitive systems are
-Group studies of patients: important for establishing whether given region is critical for performing given task
What are the advantages of using animal models in neuropsychology?
-Each animal can serve as its own control: before lesion compared to after lesion
-Possible to use groups of animals without lesion or groups of animals with lesion in different location
What are disadvantages of animal models in neuropsychology?
-Not all cognitive functions can be studies in animals
-Not all cognitive functions can be studied at same level in animals
What are the 4 causes of elicited brain damage often used in animal models in neuropsychology?
-Aspiration of brain regions by using suction device
-Transection: cutting discrete white matter bundles
-Neurochemical lesions: inserting toxins in neurons so they get killed
-Reversible lesions: pharmacological manipulations or colling to temporarily disrupt neural activity
What can be a cause of virtual or temporary damage?
Transcranial magnetic stimulation (TMS)
What is transcranial magnetic stimulation (TMS)?
-Results rather small and short
-Usage of coil with wire carrying electric current
–>Rapid change when current on, creating magnetic field
–>Magnetic field induces current in nearby neurons, causing them to generate action potentials
–>This disrupts cognitive function that neurons may be doing at that time
–>Measuring cognitive function by asking patients to perform task
-Not harmful, but some people excluded
What are advantages of TMS in comparison to natural damage?
-No reorganization or compensation
-Can be used to determine timing of cognition
-Lesion is focal
-Lesion can be moved within same participant
-Can study functional integration
What are advantages of natural damage in comparison to TMS?
-Subcortical lesions can be studied
-Lesions can be accurately localized with MRI
-Changes in behavior/cognition more apparent
-Clinical relevance is obvious
Can you use brain stimulation to enhance brain function?
-Therapeutic effects of TMS and tES when repeated a lot
-Several promising areas of investigation: mood disorders non-responsive to other treatments, OCD, revalidation after stroke
