Edexcel International A Level Biology

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8.15 Techniques to Investigate the Brain

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Techniques to Investigate the Brain

  • It is extremely difficult for neuroscientists to study the brain and find out how it works 
    • The brain is incredibly complex and very delicate and it is protected by the skull
    • Different regions work together to bring about brain function so can’t be studied in isolation
  • Specialised scanners and techniques can be used to study the brain without having to resort to surgical intervention

Computerised Tomography

  • Computerised tomography, or CT, scans produce cross-section images of the brain using x-ray radiation
    • A beam of x-rays is aimed at a patient from all angles around the body 
    • Digital x-ray detectors are used to pick up the x-rays as they exit the patient's body
    • Denser tissue absorbs more of the x-ray radiation so shows up as a lighter region on a scan
  • A scan produced in this way shows physical structures of the brain and allows visualisation of any tissue damage
    • E.g. blood is less dense than brain tissue so a CT scan can be used to locate damaged blood vessels and areas of bleeding after a patient has had a stroke
  • The scans don't directly show the functions of the regions of the brain but it is possible to link visible symptoms with the location of any tissue damage 
    • This can allow neurologists to work out which regions of the brain are responsible for which functions
  • CT scans are not recommended for pregnant patients or children due to the risks of exposure to the X-ray radiation, which is given at a higher level than in a normal X-ray
    • The risk of damage from such scans is still very low

Magnetic Resonance Imaging

  • Magnetic Resonance Imaging, or MRI, uses a combination of a magnetic field and radio waves to generate images through the body
    • The patient being scanned must remain very still while inside a large magnet
  • Soft tissues can be seen clearly using MRI, and images produced are at a higher resolution than those produced from CT scanning
  • As with CT scanning, MRI is useful for identifying areas of abnormal or damaged tissue, but only enables brain function to be analysed by linking damage on a scan with visible symptoms in a patient
  • MRI is especially useful for tumour diagnosis as tumours show up clearly in images generated in this way
    • MRI scans can therefore be used to identify and locate tumours in the brain
  • MRI scans are considerably more expensive to carry out than CT scans but do not carry the risk associated with the use of potentially harmful x-rays
    • MRI scans are often the imaging method of choice during long-term therapies
  • The magnetic field of an MRI scanner can interfere with medical devices such as pacemakers and insulin pumps, so patients with such devices cannot have MRI scans

Functional MRI

  • Functional MRI, or fMRI, functions in a similar way to MRI, making use of a magnetic field and radio waves to generate images of brain structure
  • The difference between MRI and fMRI is that fMRI scans allow brain function to be studied in real time
    • fMRI scans show the location of oxygenated blood in the brain, therefore indicating which brain regions are active at any one time
      • The scanner measures the ratio of oxygenated to deoxygenated haemoglobin
    • Patients can be asked to carry out particular actions, answer questions, or think about a specific topic while inside a scanner and the change in blood flow to regions of the brain can be assessed
      • The region of the brain associated with the activity or thought will 'light up' in the scanner 
      • This can be used in medical diagnosis e.g. searching for the cause of seizures, or in psychology research

Positron Emission Tomography

  • PET scans use radioactive tracers which collect in areas where there is increased blood flow, metabolism, or neurotransmitter activity
    • The tracer is introduced to the blood in advance of the scan so that it can be detected by the scanner
    • E.g. a radioactive tracer might be radioactively labelled glucose; glucose will be transported in the blood and will be present in high concentrations in metabolically active areas of the brain
  • The scanner can detect areas of high radioactivity, and so the movement of the tracer through the body and any accumulation of tracer in the brain can be seen
  • The amount of radioactive tracer present in a brain region can indicate whether that region is active or inactive
    • This has been useful in building an understanding of specific diseases such as Alzheimer's where brain activity in certain regions decreases
  • Neurologists can use the images to study the structure and function of the brain in real time 

types-of-brain-scan

Some types of scan show only structure, while other allow the study of structure and function in real time

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Naomi H

Author: Naomi H

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.