Lesion Methods PDF

Lesion Methods 18 January 2024 20:24 Main Ideas Notes Correlation vs. causation Neuroimaging methods only allow correlational inferences about the mind and the brain. Neural activity X is related to function Y. Not possible to tell with certainty whether particular brain activity is crucial for some...

Lesion Methods 18 January 2024 20:24 Main Ideas Notes Correlation vs. causation Neuroimaging methods only allow correlational inferences about the mind and the brain. Neural activity X is related to function Y. Not possible to tell with certainty whether particular brain activity is crucial for some aspect of the mind An example: memory fMRI activation in medial and lateral parietal cortex typical during memory retrieval. However, parietal lesions do not typically affect retrieval ability ○ For example, seeing brain activity during a memory test doesn’t prove that area is responsible for memory. A lesion study might show that damage to that area actually disrupts memory, suggesting causation. An understanding of causation is crucial for developing treatments for brain-related issues. This topic has implications for how we interpret brain-imaging data and make conclusions about brain functions. It raises questions like, "Does heightened brain activation lead to better cognitive function, or is it an accompanying effec t?" Human intracranial recordings Recording activity directly from within the brain allows easier localisation of activity (inverse problem is reduced) However, still not causal Patients with epilepsy may have these recordings to locate the origin of seizures. They allow for more detail than external EEG but are invasive and used only when necessary Animal recording Single- and multi-unit recording in animals also do not allow definitive causal inferences Help us learn about brain functions without the same risks posed to human subjects. Animal studies also face challenges in translating findings directly to human patients. Many major discoveries, like the role of the hippocampus in memory, come from animal research. However, they can’t provide clear-cut evidence of causality on their own. Ethical concerns are also important, emphasizing the need for responsible research practices Drawing Causal Inferences aim is to interfere with brain activity and see how it changes behavior to draw causal inferences. Pharmacological manipulations change brain chemistry to study the resulting behavioral effects. Lesion studies involve observing behavioral changes when specific brain areas are damaged. These interferences provide much stronger evidence of brain areas' roles than simple observations. For instance, studying patients with specific brain injuries helped us understand speech areas. Natural Brain Lesions Natural lesions are brain damages from strokes, injuries or diseases, not caused deliberately for study. Observing these helps to understand brain function responsibilities. An example is studying patients with aphasia, who have language difficulties due to brain damage. These real-world cases provide insights that controlled studies cannot achieve. However, these damages are random and not controlled, which complicates drawing conclusions Neuropsychology Neuropsychology uses brain damage to learn about mental processes. Studies of people with brain damage have helped map language to the left hemisphere. Understanding how damage affects speech or comprehension has led to improved rehabilitation. Comparing brain function before and after lesions assists in understanding the brain’s adaptability. Damasio's study on Phineas Gage is a famous example, linking frontal lobe damage to personality changes. Summary PSYC0031 Cognitive Neuroscience Page 1 Notes Single Case Studies Individual cases can highlight very specific cognitive processes linked to particular brain regions. They can offer deep insights into how complex brain functions are but may not be generalizable. The famous case study of H.M. taught us about the role of the hippocampus in forming new memories. Such single case studies push forward our understanding one unique individual at a time. They provide detailed examination opportunities that group studies might mask. Group studies Patients are grouped based on similar injuries or deficits for comparative studies. Structural MRI helps researchers see and categorize the damage across individuals. Data from such groupings can be aggregated to strengthen the validity of observations. It reduces the variability seen in single case studies and enhances general conclusions. A classic group study might focus on patients with frontal lobe damage to understand this area's role in decision -making. Exploring both associative and dissociative cases within a group could reveal connections between different cognitive functio ns and brain areas. Associations vs. Dissociation Associative evidence tells us when two functions are linked to the same brain region. Dissociative evidence is more valuable, showing when a brain area relates to one function but not another. For instance, if a patient can still speak but not comprehend language, it suggests different brain areas are involved in the se processes. Dissociative evidence can refine our understanding of the brain’s division of labor. Probing such specialized functions helps in crafting specific theories of how the brain works. Problems with Natural Lesions Obstacles include unpredictability of lesions and their diverse impacts on individuals. People with natural lesions might also experience brain recovery that can cloud study results. Availability of subjects with specific, systematically located lesions is rare and unpredictable. Studies must account for unique individual differences in brain structure and plasticity. Having sufficient and diverse subjects can be a challenge in natural lesion studies. Despite these issues, natural lesions have provided foundations for much of what is known about the brain. Animal Lesion Studies Ethical considerations are paramount; we aim to minimize harm while maximizing the knowledge gained. Animal studies are key for controlled experiments that would be unethical in human participants. They provide insights by precise targeting and lesioning of brain regions in a controlled setting. These studies can be designed to mirror human conditions, such as stroke or degenerative diseases. Animal models have been instrumental in understanding diseases like Parkinson’s and Alzheimer’s. Ethical guidelines ensure that studies are justified, humane, and contribute significantly to science. Virtual Lesions Temporary, non-invasive virtual lesions mimic the effects of actual brain damage. Advanced techniques like TMS, tDCS, and ultrasound offer reversible ways to study the brain. Through these methods, researchers can temporarily affect brain regions to observe changes in behaviors or tasks. This slide details how we can study the importance of brain areas without causing permanent harm. Virtual lesions allow for repeated studies on the same subjects, enhancing experimental control. They contribute significantly to our understanding of dynamic brain functions in real -time TMS TMS uses strong magnets to impact brain function temporarily and non -invasively. The magnets induce an electric current in a targeted brain area, influencing its activity. Impacting the motor cortex, for example, can cause a hand or arm to twitch. TMS can selectively inhibit or enhance brain functions to assess their roles. Researchers use TMS to study cognitive processes like language or attention. This method exemplifies the innovative approaches cognitive neuroscience utilizes to understand brain -behavior relationships. Notes How TMS works An electrical current passes through a coil placed near the scalp, inducing brain activity underneath. This activity can result in perceptible outcomes, like muscle movement or temporary changes in sensory experiences. The method is helpful for probing the brain’s functional map and understanding how different regions contribute to behavior. TMS can be targeted to specific brain areas, making it a precision tool in cognitive neuroscience. Administration of TMS can influence ongoing tasks, like language processing or memory recall. Studies using TMS have helped delineate the time course of specific cognitive processes. tDCS Effects of TMS Altering activity in the visual cortex may produce visual disturbances called phosphenes. Changing the motor area's activity can result in movement, providing a direct link to brain function. TMS has also been used to disrupt normal processing, such as temporarily impairing language or memory tasks. TMS effects help deduce the localized functions of the brain’s various parts. This tool has the potential to aid in rehabilitation approaches for various neurological conditions. The insights from TMS studies extend into understanding complex cognitive tasks. Motor Cortex Applyin A study The resu These fi The dos tDCS rep Safety of TMS TMS treatment protocols are designed to ensure safety and minimize any adverse effects. Repetitive or rTMS can have potential risks, so safety guidelines are strictly followed. The most common side effects are minor and include discomfort at the stimulation site or headaches. Long-term safety of TMS is a subject of ongoing research, but current evidence supports its safe use. Institutional review boards and ethical committees oversee TMS studies to ensure participant welfare. Safety measures highlight the importance of balancing research advancement with participant care. tACS Where to Stimulate with TMS Determining the exact point of stimulation is critical for precise experimental outcomes. Structural MRI scans help in locating the appropriate area before applying TMS. Techniques for locating the target site have improved, but there is still room for refinement. Aligning TMS with a participant's individual brain anatomy increases the technique's specificity. Stimulation sites can be mapped out in relation to known anatomical landmarks or functional activities. For example, targeting the motor cortex to evoke muscle responses requires precise location techniques. Rhythms in vi The visu TMS tar These rh Underst TMS's e These in Spatial Specificity of TMS The pinpoint accuracy of TMS stimulation depends on the type of coil and technique used. Different coils can target broader or narrower areas, influencing the outcomes of the study. The target's depth also affects the specificity - deeper targets may require stronger pulses. The shape of the TMS coil (figure-eight vs. circular) can determine the focus of the stimulating electric field. Better coil design can lead to more localized effects and higher precision in research. This spatial specificity helps in distinguishing the roles played by closely situated brain regions. TUS Temporal Specificity of TMS Temporal specificity refers to the timing of stimulation, which is critical for understanding cognitive processes. Applying TMS pulses at different times can help determine the sequence of brain area activation during tasks. This specificity offers insights into how quickly different brain regions communicate. Timing TMS during a behavioral task can inform the stages of cognitive processing. For instance, stimulating the visual cortex during a visual perception task can reveal when this area is crucial. Timing is therefore just as important as location when it comes to interpreting TMS effects. Conclusions (1 Integrat A multim For exam Researc This con Electrical Brain Stimulation This technique delivers electrical currents to the brain's surface via scalp electrodes. It's a non-invasive way to modulate brain activity and study its effects on cognition and behavior. Adjusting the type, intensity, and duration of electrical currents affect the stimulation's outcome. Electrical stimulation has been used to understand things like motor control and sensation. It also serves therapeutic purposes, such as in treating depression or chronic pain. This method is one of several used to explore the brain's complex electrical signalling networks. tDCS us Anodal It's used Clinical The effe Though tACS ap By align tACS ha Adjustin For exam This me TUS use It offers TUS cou This rela Ultrasou Its deve Conclusions (2 Differen The inte Experie For inst (TMS). It encou Researc Notes es low electrical currents to subtly change neuronal excitability. tDCS can make neurons more likely to fire, while cathodal tDCS can do the opposite. d in research to enhance learning, memory, and other cognitive functions experimentally. applications include treatment trials for depression and recovery from stroke. ects of tDCS can last beyond the period of stimulation, offering insights into neuroplasticity. commonly used, the full mechanisms by which tDCS affects brain function remain a research topic. x tDCS Example g tDCS to the motor cortex can influence motor learning and performance. might measure how tDCS affects the speed and accuracy of finger movements. ulting motor evoked potentials (MEPs) can show changes in brain-motor connectivity. indings have implications for physical rehabilitation and motor skill acquisition. se-dependent nature of tDCS allows researchers to explore different intensities and effects. presents a simple and adaptable option for modulating brain activity in cognitive neuroscience. pplies alternating electrical currents to modulate brain oscillations in specific frequency bands. ning stimulation frequency with natural brain rhythms, tACS can influence cognitive states. as been utilized to explore the role of brain waves in attention, memory, and conscious perception. ng the frequency of tACS allows for targeting different cognitive processes. mple, tuning to the alpha frequency may affect visual attention and processing. ethod opens up possibilities for studying and potentially enhancing synchrony in brain networks. isual cortex ual cortex has natural rhythms, like the alpha wave, linked with visual perception. rgeting the visual cortex during low alpha states can impact visual experiences. hythms can also be influenced by external factors, such as light exposure or cognitive load. tanding rhythms in the visual cortex helps us learn how the brain processes sight. effects on these rhythms provide clues about the timing of visual processing. nsights contribute to models of how sensory information is integrated and interpreted by the brain. es high-frequency sound waves to achieve non-invasive brain stimulation. s potentially greater spatial resolution and can reach deeper brain areas than other methods. uld be used for targeted interventions in areas like the thalamus or deep cortical layers. atively new approach is still being explored for its capabilities and potential applications. und allows for precise modulation of neural circuits, creating a range of research opportunities. elopment underscores the ongoing innovation within the field of cognitive neuroscience. 1) ting data from different methods can lead to stronger conclusions about brain-behavior relationships. modal approach compensates for individual methodological weaknesses. mple, fMRI provides detailed spatial maps while EEG offers precise timing information- together they provide a fuller picture. ch must always aim for the most appropriate method to answer specific questions. nvergence of evidence from various techniques reinforces the validity of cognitive neuroscience findings. 2) nt methods can sometimes show both quantitative (how much) and qualitative (what kind) differences in brain activity. erpretation of results requires understanding the strengths and limitations of each method. nce with neuropsychological tests, brain imaging, and lesion studies complements one another. ance, seeing where the brain is active during a task (fMRI) can be compared to what happens when that area is disrupted urages a holistic view of cognitive neuroscience, where a single method doesn't tell the whole story. chers should always aim to match the research question with appropriate cognitive neuroscience techniques. PSYC0031 Cognitive Neuroscience Page 2 Conclusions (3) Critical thinking is crucial in evaluating studies based on their methods and results. Researchers should question whether the chosen method can effectively test the hypothesis at hand. The lecture advises that careful consideration should be given to the experimental contrasts used. Validating research findings through both direct and indirect evidence is essential. For instance, does a study using TMS offer enough support for a theory, or are other methods needed? Being a good scientist in cognitive neuroscience involves continuous learning and skepticism about methodologies and conclusions. Notes Notes PSYC0031 Cognitive Neuroscience Page 3 Notes Notes PSYC0031 Cognitive Neuroscience Page 4 PSYC0031 Cognitive Neuroscience Page 5