Ways of measuring the brain

4 methods of measuring the brain

• fMRI (small f, cap MRI)

• EEG

• ERP

• Post mortem

Temporal resolution

The accuracy of the scanner in relation to time, ie how quickly the scanner can detect changes in brain activity.

Spatial resolution

The smallest feature (or measurement) that a scanner can detect. Eg if a scan has a spatial resolution measured in cm, it can only detect brain activity to the nearest cm. If it has a spatial resolution measured in mm, it can detect which brain area is active much more accurately.

fMRI – functional magnetic resonance imaging

fMRI machines are specialist MRI machines that can show activity as it occurs. They work by monitoring the flow of oxygenated blood. This is possible because haemoglobin and oxyhaemoglobin have different magnetic properties.

The magnetic resonance information is automatically processed by computer, and a series of scan pictures are generated by computer, showing the oxygenated blood flow in different areas of the brain.

when a brain region is active, it will require more oxygen. The flow of oxygenated blood to that region will increase. Thus an fMRI scan can help us build up a picture of brain activity. The person having the scan can communicate with the technician verbally, and can be shown visual information, so they can carry out cognitive tasks while in the scanner. Blood flow in their brain is monitored while they carry out these tasks.

fMRI - key characteristics

1. Measures changes in blood flow that occur approximately 1-5 seconds after neural activity, giving fMRI relatively poor temporal resolution.

2. Accurate within 1-2mm of the brain (good spatial resolution)

3. Produces 3D images

4. fMRI scanners are extremely expensive to purchase and maintain, making them one of the most costly methods of studying the brain.

evaluation of fMRI - CRIED - causation

A significant weakness of functional magnetic resonance imaging (fMRI) lies in the limited ability to draw causation conclusions from the data it provides. fMRI only measures blood flow as an indirect measure of neural activity. Increased blood flow does not automatically mean a brain area is responsible for a behaviour, making interpretation difficult. For instance, increased blood flow in a particular brain region does not necessarily imply causation; it could be a result of various cognitive processes or external stimuli. This limitation restricts researchers from making definitive statements about the causal relationships between brain activity and behaviour.

Resolution (temporal)

Functional magnetic resonance imaging (fMRI) exhibits a weakness in its poor temporal resolution. fMRI has a temporal resolution on the order of seconds, meaning it cannot precisely track neural events that occur within milliseconds. The limited temporal resolution of fMRI poses challenges in studying changing cognitive processes, such as decision-making or language comprehension, where quick neural responses play a crucial role. In psychological research, this limitation underscores the importance of combining fMRI with techniques offering superior temporal resolution to achieve a more comprehensive understanding of cognitive processes and brain function.

Resolution (spatial)

A strength of functional magnetic resonance imaging (fMRI) lies in its impressive spatial resolution. Studies have shown that fMRI can detect changes in brain activity at the level of millimeters. This can provide detailed insights into the anatomical localization of the brain. For example, fMRI can precisely pinpoint the activation of specific brain regions during cognitive tasks or emotional experiences. This spatial resolution allows researchers to map brain activity with high precision. In psychological research, the heightened spatial resolution of fMRI enables the identification of brain regions associated with various cognitive functions, emotions, and disorders.

Invasiveness

One notable strength of functional magnetic resonance imaging (fMRI) is its non-invasive nature compared to other neuroimaging techniques. This characteristic enhances the applicability of fMRI in psychological research, enabling investigations into neural processes underlying various cognitive functions and disorders while prioritizing participant well-being and ethical standards. Compared with PET scans, fMRI is non-invasive because it does not require radioactive tracers. An fMRI would only require laying in a small space for a period of time. Some patients can find it claustrophobic and noisy (the magnets in the machine clank loudly!) but overall the non-invasiveness of fMRI not only ensures participant safety and comfort but also facilitates larger sample sizes and longitudinal studies, as it is more feasible for individuals to undergo multiple scans.

Expense

One downside of using functional magnetic resonance imaging (fMRI) is its high cost. The actual device itself is expensive to purchase, maintain, and operate. This financial barrier limits access to fMRI technology for many researchers and institutions. The high expense of fMRI testing also restricts the sample size of studies, which can affect the generalizability and reliability of findings in psychological research. While fMRI offers valuable insights into brain activity and cognitive processes, its costliness hampers its widespread use and accessibility in psychological research.

Diagnosis

One notable strength of functional magnetic resonance imaging (fMRI) lies in its potential as a diagnostic tool. For instance, fMRI has been employed in various clinical settings to detect abnormalities in brain function associated with neurological and psychological disorders such as schizophrenia, depression, and Alzheimer’s disease. Through fMRI, researchers and clinicians can identify specific patterns of brain activity that are indicative of certain conditions, aiding in early diagnosis and treatment planning. This diagnostic capability enhances the utility of fMRI not only in clinical practice but also in psychological research. By explaining the neural picture of different disorders, fMRI contributes to a deeper understanding of their underlying mechanisms, paving the way for more targeted interventions and therapies.

EEG – Electroencephalogram - What is it and how does it work?

EEGs do not involve you being put into a machine, but require electrodes to be attached to the scalp. This can be seen in the picture below. Some machines are built to fit on like a swimming cap (called skull cap) and pick up the information they need from that.

They work by picking up on and recording the electrical activity of the brain. So, think back to when we learnt about neurons – remember, their function is to conduct electrical impulses. Each electrode works by detecting electrical activity immediately below it, so the more electrodes you have the more electrical activity can be picked up on. Modern EEG systems typically use dozens to hundreds of electrodes placed across the scalp. This provides an overall account of activity in the brain, as it tells you how much activity is going on and will identify the type of electrical activity that is happening.

EEG - Key characteristics

1. Shows activity within milliseconds of the activity happening (good temporal resolution)

2. The more electrodes there are the more accurate the reading: however, electrodes can only measure the activity at the surface of the brain, and cannot assess how deep the activity is, or where exactly it is happening. Also, a single electrode will be monitoring thousands of neurones in the brain area below the electrode, so activity can’t be narrowed down to specific neural connections (poor spatial resolution)

3. And, as you can see above, the results of an EEG require a trained specialise to understand and interpret them.

EEG - causation

Point: It can be difficult to determine exactly what psychological process is responsible for observed patterns of brain activity because many processes occur simultaneously.
Evidence: An EEG uses electrodes attached to the scalp that detect brain activity close to it. The brain will be process multiple things at once, and indeed sometimes we don’t even realize the brain is processing/ actioning a stimulus or behaviour.
Explain: While EEG detects changes in brain waves, it is difficult to determine whether these changes are caused by the stimuli being presented or other factors that are causing brain activity.

EEG - (spatial) resolution

Point: A weakness of EEGs is their poor spatial resolution.
Evidence: EEG electrodes measure electrical activity at the scalp surface.
Explain: Thus we can only learn the rough location of brain activity, as the EEG cannot tell us how deep within the brain it is occurring. Behaviours such as memory would be difficult to localise using this method due to the areas typically associated with memory being so far from the surface of the cerebrum.

EEG - (temporal) resolution

Point: A strength of EEGs is their excellent temporal resolution.
Evidence: Due to the fact that the electrodes detect activity very quickly, an EEG offers excellent temporal resolution, capturing rapid changes in brain activity within milliseconds.
Explain: EEGs ability to track real-time brain changes allows researchers to see slight changes in activity as they happen. For example, slight changes in sleep stages or the pattern of an epileptic seizure, thus leading to a better understanding of that behaviour. In this respect they are better than fMRIs, which might miss rapid, transient changes.

EEG - expense

Point: A strength of EEGs is their low cost in comparison to other methods of measuring the brain.
Evidence: In comparison to an FMRI, EEG equipment is relatively affordable and requires minimal maintenance. Unlike expensive neuroimaging techniques like fMRI or PET scans, EEG offers a cost-effective option for studying brain function.
Explain: The affordability of EEG technology expands opportunities for researchers to conduct large-scale studies, facilitating greater access to brain research across diverse populations and settings in psychology.

EEG - diagnosis

Point: A strength of EEGs is their usefulness in diagnosing certain conditions.
Evidence: EEGs are used clinically to diagnose various neurological conditions, such as epilepsy and sleep disorders, which show characteristic patterns of brain activity.
Explain: In psychology, EEG diagnostics aid in understanding the neural underpinnings of mental health conditions, informing treatment strategies and enhancing patient care.

ERP – event related potentials - What is it and how does it work?

These scans use the same equipment of EEGs, ie the electrodes and the ‘ponytail’ of wires leading to a computer, but they process the information in a more sophisticated way. This means that ERPs can tell us more accurately what is happening in the brain. On it’s own an EEG doesn’t actually tell us that much – the brain is processing so much information at any one moment that we can’t use an EEG reading to say a specific activity in the brain relates to a specific task or stimulus. To overcome this, the technology has been developed and the updated version is called an ERP scanner.

• Patients are presented with the same stimulus repeatedly (eg an image or a spoken word)
• The timing and type of stimulus is carefully controlled
• EEG readings are generated each time
• The electrical patterns are analysed statistically to identify the electrical activity associated specifically with the stimulus
• This means that ongoing background activity and noise can be accounted for
• The excellent temporal resolution of the EEG is maintained. Waves of electrical activity seen 100ms after stimulus show cognitive processing.
• Spatial resolution is improved to cm (but not mm, this is because the sensors are measuring activity at the surface, so signals are averaged across relatively large brain areas).

ERP - research in action

Costa, Braun & Birbaumer (2003) used this method to record responses to nude pictures of both sexes in young people (19-29 years). When asked abut how they felt, men generally said they were aroused by the nude female pictures, whereas women mostly reported to having neutral feelings to both male and female pictures (self report measure- what could be a problem with this measure?). However, when the researchers examined the ERP’s, they found that participants had a much higher response to nude pictures of the opposite sex than they reported. Suggesting that this method of measuring activity is more accurate and less biased than other research methods adopted by psychologists.

Evaluation- CRIED

Because ERPs are recorded in response to a controlled stimulus, researchers can more confidently identify brain activity associated with that stimulus than with standard EEG recordings.

Causation

Causation. ERPs can detect brain responses to specific stimuli with high temporal precision. By analyzing ERP waveforms, ERPs allow researchers to identify neural responses associated with specific stimuli. This capability allows psychologists to investigate the mechanisms underlying cognitive processes and behaviours, advancing our understanding of brain-behaviour relationships and informing interventions for cognitive disorders.

Temporal resolution

Temporal resolution. ERPs offer excellent temporal resolution, capturing rapid changes in brain activity within milliseconds. ERP’s ability to track real-time brain dynamics enables precise analysis of cognitive processes, including perception, attention, and decision-making. In psychology, ERP’s temporal resolution facilitates the investigation of dynamic brain activities underlying complex behaviors, contributing to a deeper understanding of human cognition and behavior in real-time contexts.

Spatial resolution

Spatial resolution. ERPs have limited spatial resolution compared to neuroimaging techniques like fMRI. ERP recordings measure electrical activity at the scalp surface, resulting in low spatial precision and difficulty in pinpointing the exact brain regions involved. ERPs retain the relatively poor spatial resolution of EEG recordings because electrical activity is still measured from the scalp. The limited spatial resolution of ERPs restricts the ability of psychologists to precisely localize neural activity, which may limit insights into the neural networks underlying cognitive functions and behaviours.

Inconvenience

Inconvenience. While not invasive, many people find ERPs inconvenient and restrictive. It require electrodes to be attached to the scalp, which can be uncomfortable for participants. It involves sitting still and repetition of tasks. This may limit long-term monitoring and may deter some individuals from participating in studies. In psychology, techniques like ERPs may restrict research participation and hinder the exploration of brain activity over extended periods, impacting the depth of understanding of cognitive processes and disorders.

Expensive

Expensive. ERPs require minimal equipment and can be conducted using standard EEG setups. Compared to expensive neuroimaging techniques like fMRI or PET scans, ERPs offer a cost-effective option for studying brain function. The affordability of ERPs expands opportunities for researchers to conduct large-scale studies, facilitating greater access to brain research across diverse populations and settings in psychology.

Diagnosis

Diagnosis: ERP is not really a diagnostic tool, but an EEG is. ERPs are instead useful in studying cognitive processing abnormalities, like epilepsy, but it wouldn’t be use to diagnose epilepsy.

Post mortem examinations - What is it and how does it work?

Clinicians will open up the skull and examine the brain by observing and cutting into it with the aim of identifying any abnormalities that might explain the behaviours of people when they were alive. For example, they may investigate individuals who experienced unusual neurological or psychological symptoms to identify if there was anything in their brain structure that could be related to, or even cause the issues from their living life.

Key characteristics

1. Post-mortem examinations can only be conducted after death, meaning researchers cannot observe brain activity as behaviour occurs.

2. You can view the inactive brain in extreme detail, you would only be limited by the magnifying glass/ microscope you have access to.

Evaluation - causation

Causation: One of the main limitations of post-mortem examination is the issue of establishing causation. The deficit a patient displays during their lifetime (e.g. an inability to speak) may not be linked to the deficits found in the brain after death (e.g. a damaged Broca’s area). The deficits reported could have been the result of another illness, and therefore psychologists are unable to conclude that the deficit is caused by the damage found in the brain.

Another issue is that there are many extraneous factors that can affect the results/conclusions of post-mortem examinations. For example, people die at different stages of their life and for a variety of different reasons. Furthermore, any medication a person may have been taking, their age, and the length of time between death and post-mortem examination, are all confounding factors that make the conclusions of such research questionable.

Detailed examination

Detailed examination: Spatial Resolution: However, one strength of post-mortem examinations is that they provide a detailed examination of the anatomical structure and neurochemical aspects of the brain that is not possible with other scanning techniques (e.g. EEG, ERP and fMRI). Post-mortem examinations can access areas found deep within the brain like the hypothalamus and hippocampus. They allow direct examination of brain tissue and neurochemistry in far greater detail than scanning techniques.

Invasive

Invasive? While post-mortem examinations are ‘invasive’, this is not an issue because the patient is dead. However, there are ethical issues in relation to informed consent and whether or not a patient provided consent before his/her death. Furthermore, many post-mortem examinations are carried out on patients with severe psychological deficits (e.g. patient HM who suffered from severe amnesia) who would be unable to provide fully informed consent, and yet a post-mortem examination has been conducted on his brain. This raises severe ethical questions surrounding the nature of such investigations.