Investigating the Brain Flashcards
Histology (neuronal level)
- Study of the microscopic structure of biological material
- It involves examining extremely thin slices of tissue under a microscope
What is neuronal staining (histology)?
Involves staining thin slices of brain tissue with chemicals and placing them under a microscope to visualise the structure of neurons
How was neuronal staining carried out in 1873?
Camillo Golgi developed the ‘black reaction technique’ - he used potassium dichromate to harden brain tissue, then soaked it in a silver nitrate solution. The reaction between the chemicals formed fragments of silver chromate, which then clustered around the cell membrane staining it black. He could not differentiate between different neurons as they were all stained the same colour, and only a few neurons could be visualised at a time
Who was Marian Diamond?
She used histological methods to produce the first evidence of neuronal plasticity - the brain can be altered by experience
She concluded the 5 biggest factors were diet, exercise, challenge, newness and love
Evidence for this was found by studying rats living in both enriched and impoverished conditions. Enriched rats had far more glial cells and a heavier and 6% thicker cortex than impoverished rats
What were the results when comparing Einstein’s brain with other men?
Compared to healthy controls, Einstein’s brain had significantly more glial cells per neuron in Broadman’s area 39, the left part of the parietal cortex. This area is thought to be involved in mathematical ability and imagery
What is brainbow / electroencephalography (EEG) (neuronal level)?
- Synaptic activity generates subtle electrical impulses (postsynaptic potentials)
- Groups of neurones firing in synchrony generates an electrical field that can be measured through the scalp
- EEG is a method for monitoring electrical activity in the brain (encephalon = brain)
- It monitors general activity over time providing insights into different states of arousal, including sleep
- It has good temporal resolution as the signal is directly related to instantaneous neuronal activity
- However, this method has poor spatial resolution as the signal in the scalp is often the sum of signals from different brain sources whose locations are difficult to infer
- As EEG can be time-locked to an external event, the potential can be measured when subjects are exposed to certain events. This measurement is called event-related potential (ERP)
What was the result of using EEG and showing subjects photos of human faces?
The human face elicited a consistently larger negative ERP component. This is the N170 signal specific to human faces
Brain damage (regional level -> function)
- Changes in behaviour and cognitive function that result from brain damage allow us to infer the function of the affected brain region when it is not damaged
- Common causes of brain damage are strokes, traumatic brain injuries and epilepsy
What are the two types of stroke?
- Ischaemic - a clot blocks blood flow to an area of the brain
- Haemorrhagic - bleeding occurs inside or around the brain
What is Broca’s aphasia? (brain damage)
Damage to left inferior frontal gyrus, leaving the patient with intact language comprehension but impaired speech production, meaning they cannot string together sentences
What is Wernicke’s aphasia?
Damage to the border of the left temporal parietal junction, leaving the patient with intact speech production but impaired language comprehension, meaning they can make syntactically correct sentences but with a meaningless string of words
What is position emission tomography (PET) (regional level -> functional level -> imaging activity)?
- Harmless radioactive tracers are injected into the bloodstream
- The brain is scanned by radiation detectors while the participant is performing a task
- The areas of the brain that are involved in the task will require more energy, so there will be greater blood flow to these areas. As a result there will be more radioactive tracer in more active parts of the brain
- This method can infer which brain regions are involved in the task
- This relies on blood volume in certain areas
What is magnetic resonance imaging (MRI) (regional level -> functional level -> imaging activity)?
- MRI involves a strong magnetic field which is applied and ceased
- Energy released by molecules in tissue as a result of this pulse respond differently and give different signals
- This allows differentiation of different brain tissues
- MRI provides structural images and information about brain activity
What is functional MRI (fMRI) (regional level -> functional level -> imaging activity)? Example: the blood oxygen level dependent response (BOLD response)
- Oxygen delivered to neurons by haemoglobin
- An increase in activity in an area leads to increased oxygen demand, and as a result there is an increase in blood flow to that region
- Oxygenated haemoglobin -> diamagnetic
- Deoxygenated haemoglobin -> paramagnetic
- The difference in magnetic properties of haemoglobin leads to small differences in MRI signal depending on the level of oxygenation
- Based on the level of blood oxygenation, which varies, one can infer different levels of ‘activity’
What is computerised tomography (CT) (regional level -> structural level)?
- A series of X-rays are sent out from different angles
- A computer combines the X-rays into a series of horizontal sections of the brain
- X-ray absorption varies with tissue density; bones absorb the most and appear white, cerebrospinal fluid absorbs least and appears black, and grey/white matter is intermediate and appears grey
- The process is quick and easy so good for patients in hospital
- However, the tissue contrast is not as good as MRI so it is not good for research
- Lots of radiation can also be harmful
