Ways of Studying the Brain
Overview of Brain Research in Neuroscience
The brain serves as the central focus of neuroscience, providing essential insights into the biological foundations of human behaviour and mental processes.
Research scientists utilise various methods to study the functions of different brain regions, which can be broadly categorised into two approaches:
Scanning the living brain: Monitoring patterns of electrical activity or blood flow associated with specific tasks.
Studying deceased brains: Conducting anatomical investigations to find physical reasons for behaviours observed while the patient was alive.
Post-Mortem Examinations
Role: Post-mortem examinations involve examining the brain after death to establish the underlying neurobiology of specific behaviours. Researchers study individuals who displayed behavioural abnormalities or brain damage symptoms while alive and look for structural differences that are absent in healthy control individuals.
Examples:
Broca's Area: An early use of this technique was by Paul Broca with his patient 'Tan'. Tan exhibited significant speech problems during his life; a post-mortem revealed a lesion in an area now known as Broca’s area, which is critical for speech production.
Memory: Post-mortem studies identified structures involved in memory. Jacopo Annese conducted a post-mortem on Henry Molaison, confirming that his inability to form new memories resulted from lesions in the hippocampus
Psychiatric Disorders: These studies link conditions like schizophrenia and depression to brain structure. For instance, post-mortem research found reduced numbers of glial cells in the frontal cortex of patients who suffered from depression (Cotter et al., 2001).
Evaluation of Post-Mortem Examinations:
Strengths:
They allow for more detailed anatomical and neurochemical examinations than non-invasive techniques like fMRI or EEG. Researchers can access deeper regions such as the hypothalamus and hippocampus.
According to Harrison (2000), they have been central to understanding schizophrenia by uncovering structural abnormalities and neurotransmitter system changes, leading to more accurate clinical diagnoses.
Limitations:
Confounding variables: Factors such as the cause of death, the stage of the disease, the length of the post-mortem delay (time between death and examination), drug treatments, and age at death can influence results.
Retrospective nature: Because the subject is deceased, researchers cannot follow up on findings or observe the real-time relationship between brain abnormalities and cognitive functioning.
Functional Magnetic Resonance Imaging (fMRI)
Role: fMRI measures changes in brain activity by detecting fluctuations in blood flow and oxygenation. Increased neural activity in a specific area creates a higher demand for oxygen; the brain responds by increasing blood flow (delivered via red blood cells) to that region.
Methodology:
Researchers produce maps showing which brain areas are active during mental processes.
A common experimental design involves a participant alternating between a task state (e.g., viewing a visual stimulus for ) and a control state (e.g., having eyes closed for ).
Data is analysed to find brain areas where activity changes consistently with the stimulus presentation.
Evaluation of fMRI:
Strengths:
Non-invasive: It does not require instruments to enter the body and does not use harmful radiation.
Objective and Reliable: It provides scientific measurements of psychological phenomena that might not be accurately captured by verbal reports.
Limitations:
Indirect measure: It measures blood flow rather than direct neural activity, meaning it is not a purely quantitative measure of mental activity.
Localisation focus: Critics argue it ignores the networked nature of the brain by focusing on specific active areas rather than the communication between regions.
Electroencephalogram (EEG)
Role: EEG measures electrical activity by using electrodes placed on the scalp to detect small electrical charges resulting from brain cell activity. These signals are graphed over time.
Clinical Applications: Used to detect disorders such as epilepsy (evidenced by spikes in electrical activity) and Alzheimer's disease or other brain injuries (evidenced by an overall slowing of activity).
Basic EEG Patterns:
Alpha waves: Occur when a person is awake but relaxed (rhythmical pattern).
Beta waves: Occur during physiological arousal (low amplitude, fast frequency) and during REM (Rapid Eye Movement) sleep.
Theta waves: Occur as a person moves from light sleep to deeper sleep.
Delta waves: Occur during deep sleep stages.
Evaluation of EEG:
Strengths:
Real-time recording: Unlike static scanning images, it records activity as it happens, allowing for precise measurement of tasks.
Diagnostic utility: Essential for diagnosing epilepsy by capturing the sudden changes in neural activity that cause seizures.
Limitations:
Superficial reach: It can only detect activity in superficial regions (the cortex) and cannot reach deeper structures. While electrodes can be implanted in non-humans for depth, this is ethically impermissible in humans.
Poor spatial resolution: Signals can be picked up by multiple neighbouring electrodes, making it impossible to pinpoint exact sources of activity in adjacent locations.
Event-Related Potentials (ERP)
Definition: ERPs are very small voltage changes in the brain triggered by specific stimuli or cognitive processing. Because these signals are faint and buried beneath background neural 'noise', the stimulus must be presented many times. These responses are then averaged to cancel out extraneous activity.
Classification of ERPs:
Sensory ERPs: Occur within the first of stimulus presentation; they reflect the initial response to the physical characteristics of the stimulus.
Cognitive ERPs: Occur after the first ; they reflect how the subject evaluates the stimulus and demonstrate information processing.
Evaluation of ERPs:
Strengths:
Continuous and precise: They allow researchers to see how processing is affected by specific experimental manipulations.
Covert monitoring: They can measure the processing of stimuli even if the person does not provide a behavioural response, which is useful for certain patient populations.
Limitations:
High trial requirement: Because the signals are so small, a large number of trials are required to generate meaningful data, limiting the types of questions that can be answered.
Restricted area: Only strong voltage changes on the scalp are recorded, meaning the technique is largely restricted to the neocortex and cannot record deep brain activity.