Lesson 4(1) Brain Information Acquisition Methods
Methods to Obtain Brain Information
Brain Damage (Lesion Studies)
One of the oldest methods for studying the brain involves examining brain damage, also known as a lesion. A lesion refers to an area of the brain that is missing, removed, damaged, or destroyed. This method operates on the principle that if a specific brain area is damaged and a person's behavior changes as a result, that area likely contributed to the lost function. Lesions can be either naturally occurring (e.g., due to stroke, trauma, disease, or developmental anomalies) or experimentally induced in animal models.
How Information is Gained
When a person experiences brain damage that alters their behavior (e.g., inability to speak, memory loss, impaired planning), and subsequently dies, their brain can be examined post-mortem. By identifying the exact location and extent of the damage through techniques like histological analysis, researchers can infer the function performed by that missing or destroyed area. For instance, if damage to a particular cortical region consistently leads to expressive aphasia, it indicates that the damaged region had a critical role in language or speech production. The fundamental assumption is that the behavioral deficit is directly caused by the loss of function in the lesioned area.
Examples
Hippocampus Damage: Patient H.M., who had his hippocampus surgically removed to treat severe epilepsy, could no longer form new declarative memories (anterograde amnesia), while his old memories and procedural memory remained relatively intact. This profoundly demonstrated the hippocampus's crucial and specific role in the consolidation of new long-term memories.
Stroke: Damage to Broca's area (typically in the left frontal lobe) due to a stroke can result in Broca's aphasia, where individuals struggle with speech production but often maintain language comprehension. This links Broca's area to speech articulation and grammatical processing.
Phineas Gage: An individual who had a large tamping rod pass through his frontal lobe suffered severe damage, primarily to the ventromedial prefrontal cortex. While his cognitive abilities remained largely intact, he showed profound changes in personality, emotional regulation, and executive functions like planning and foresight. This provided early evidence for the frontal lobe's involvement in these complex functions.
Limitations of Lesion Studies
Causality vs. Correlation: While strong, inferring causality can be complex as damage might affect interconnected neural networks rather than just a single isolated function.
Individual Variability: The precise location and extent of lesions vary greatly among individuals, making direct comparisons challenging.
Plasticity and Compensation: The brain's ability to reorganize and compensate for damage can mask or alter the direct effects of the lesion.
Ethical Considerations: Intentional lesioning is generally not performed on humans but is a valuable technique in animal research.
Transcranial Magnetic Stimulation (TMS)
Transcranial Magnetic Stimulation (TMS) is a non-invasive neuroscientific technique that allows researchers to temporarily disrupt or modulate the functioning of specific brain areas, effectively creating a temporary, reversible