Readings 1 Flashcards
Vaidya et al 2020: Lesion studies in Contemporary Neuroscience
Purpose: compare different non-invasive methods
Conclusion: Multifaceted approaches allow for more clear understanding of brain functions related to regions - lesion studies are still relevant and important in addition to modern imaging methods.
This article shows that Neuropsychology - and more specifically, lesion-behavior mapping - is best studied through a multifaceted approach that takes into account termination, correlation, and manipulation. Each approach has specific advantages and limitations, and all converge to provide a more comprehensive picture of brain function.
- differences between single and double dissociation
- single dissociation: a lesion in a brain region is disrupting function x but not function y
- x and y are independent, and that region is necessary for the function of x but not y
- evident only in 1 patient
- double dissociation uses 2 manipulations (2 lesions, in different brain regions)
- need at least 2 patients to compare
- lesion 1 effects function 1 but not function 2, while lesion 2 effects function 2 but not function 1
- confirms that the processes are independent, and occur in different parts of the brain
- help us localize functions to brain regions.
- Key word for this diagram is necessity.
- how neuroscientists attempt to link functionality to a specific region
- ex: lesion in Broca’s area shows a low performance in producing speech, but a lesion in Wenicke’s area shows a low performance in comprehension or speaking coherently
- even though someone with Broca’s aphasia cannot produce speech, the person can still comprehend speech; however, someone with Wernicke’s aphasia can produce speech, cannot comprehend it
- double dissociation is stronger evidence than a single dissociation
- performance of a task relies on the function of region B
- Region B processes inputs that come from region A. Region B processes inputs coming from Region A and C, however, the input coming from region C is not as important for performing the task at hand.
- When region C was temporarily disrupted, there was a disturbance of region B, resulting in poor performance.
- However, when region C was permanently lesioned, region B was able to compensate for the loss of input, and no deficit was seen in performance.
- Finally, if region B is permanently lesioned, there will be an irreversible deficit in performance.
- explains the differences that permanent lesions and temporary inactivation of regions have on performance
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termination: requires the permanent destruction of some brain region or pathway causing an irreversible change in function
- observe long-term consequences of brain damage, as opposed to short-term manipulations, and also accounts for neural plasticity in responding to a brain injury
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manipulation methods: temporary and reversible changes in neural activity or region of the brain
- valuable and differs from chronic lesions because oftentimes chronic lesions display compensatory processes as the brain reroutes to maintain as much of its previous function as possible
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correlation: measuring brain activity, as well as finding an association between brain activity, behavior, and the task at hand
- we won’t be able to know which region is crucial for which activity
- Triangulation of these three methods is a way of combining them to allow us to get a more comprehensive understanding of brain functions.
- All three types of studies, terminative, correlative, and manipulative, serve to reinforce one another’s theories of localization; this is used to strengthen the results and relationships between localized brain regions and function.
Coltheart 2017: The assumptions on which Neuropsychology stands
- cognitive neuropsychology: branch of cognitive psychology which seeks to draw conclusions about theories of some domain of cognition from studies of people with cognitive impairments in that domain
- Conclusion: All 4 assumptions remain important for 21st century cognitive neuropsychology. (supports Caramazza’s idea)
Coltheart 2017
- List and describe the assumptions of Neuropsychology
- Among the principles of Neocortical Functions, the “Hierarchical Organization” of the Nervous System is one of them. How does it relate to the assumptions of Neuropsychology?
- fractionation assumption: brain damage results in the selective impairment of certain parts of cognitive processing
- modularity assumption: cognition depends on the functioning of a number of independent processing units
- transparency: cognitive systems of a brain-impaired person is fundamentally the same as a “normal” person except for “local” modification of the system
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universality: model is true of “normal” human brains in general -> generalization of results in a study to the larger population
Hierarchical organization consists of a primary area that projects to a secondary area then a tertiary area. Each area occupies a specific position/function. It is important in describing the connectivity of the brain, and how they tie together to make our unified perception of reality.
Parkin et al 2015: Neuron- Non-invasive Human Brain Stimulation in Cognitive Neuroscience A Primer
- Purpose: compare different non-invasive methods
- TMS- suprathreshold stimulation to disrupt ongoing activity and induce plasticity
- single pulse is largely excitatory, repetitive is inhibitory
- TES- just plasticity
- “three goals of using tES in cognitive studies: one is to explore the contributions of the areas to a function, the second is to understand the physiological mechanisms of these effects, and the third is to enhance cognitive function”
- TMS- suprathreshold stimulation to disrupt ongoing activity and induce plasticity
- TMS with EEG- used in studies with vision and attention
- TMS and MRI- confirmative, or can show activation in distal regions
- TMS and PET- able to show detailed cortical to subcortical distal effects.
- Types of TES:
- tDCS: mainly used to modulate excitation and/or inhibition, and to improve and in some ways alter cognitive functioning.
- tACS: goal of changing oscillatory brain states.
- tRNS: induce excitation and resulting plasticity.
Figure 2 is showing the classic experiment of TMS interference.
TMS was applied before and after the visual stimuli. Masking of the first trigram produced by the presentation of a second trigram can be unmasked by TMS suppression of the second trigram.
Subjects adapted to a combination of colors and orientation then three TMS pulses were administered. The figure shows the activation states of the neurons tuned to green and red at various stages of the TMS adaptation. Before adaptation both neural groups were at baseline activity. After adaptation to red, neurons tuned to green are more excitable than neurons tuned to red. This outcome is reversed with TMS.
Fornia, L., et al 2020: Direct Electrical Stimulation of Premotor Areas: Different Effects on Hand Muscle Activity during Object Manipulation
- #### Purpose: To see if direct electrical stimulation of the premotor cortex affects the ability to execute a hand manipulation task (HMt) and discover how involved specific premotor cortex areas are in hand object interaction.
- Conclusion: DES impaired dexterous hand movements in two areas of the PreCG - the vPM and dPM. This aids in identifying more specific regions responsible for more precise and specific movements.
- Strengths/Limitations of Study:
- Direct electrical stimulation of premotor areas: different effects on hand muscle activity during object manipulation
- Neuroanatomy: dPM, vPM (dorsal and ventral premotor)
- Direct Electrical Stimulation (DES) - applied to premotor cortex significantly impaired hand manipulation task execution.
- Stimulation of vPM caused complete task arrest and clumsy execution due to muscle suppression.
- Stimulation of dPM caused complete task arrest because hand muscles were not engaged in task
- Hand Manipulation Task (HMt) - Patient had to grab a cylindrical handle with thumb and index finger in a pincer grasp and then held it, rotated the handle, and released it.
Figure 1:
(A) EMG activity from muscles recorded during task. APB EDC, and FDI are different hand muscles. Green line represents when participant reached for object.
(B) top image: Red dots show effective (DES during task is associated with EMG patterns of activity and behavior on task) sites. Black dots show ineffective (DES during task is not associated with EMG pattern and behavior on task) sites.
Effective means DES changed EMG pattern and behavior on task.
