Brain anatomy Flashcards
corpus callosum
White matter tracts (numerous axons) connecting the two hemispheres
grey matter
- On outer part of brain
- Cerebral cortex - At the level of micro-structure, the cortex is made of bodies of nerve cells- neurons.
white matter
Situated under the grey matter.
White matter is made of the long elongated part of the nerve cells- axon.
gyrus
Plateau on cortical surface
sulcus
Fold/ditch in cortical surface - major sulci also referred to as fissures
body/soma of neuron
Part of grey matter
axon of neuron
- Part the white matter
- Axons are covered in a protective layer of myelin - speeds up transmission
- The (white) appearance of white matter comes from the light colour of myelin.
intercallosal transfer
The electrical impulses that travel from neurons in one hemispheres and reach neurons in the other hemisphere via corpus callosum
axial slice
Side-side/ear-ear
coronal slice
Top-bottom
sagittal slice
Front-back
cytoarchitecture
- Brodmann found that cortical regions vary in the detailed cellular structure (types of neurons) and cellular arrangement (number of layers, density)- this is referred to as cytoarchitecture and ways neurons laid out
- Using this as a criterion, Brodmann divided the cortex into a number of areas
- Many of these areas turned out to serve specific functions (e.g. primary visual and auditory cortices, primary motor cortex)
control of basic physiology
- Basic physiological and metabolic processes are controlled by groups of neurons in the brainstem, including thalamus and hypothalamus
- These are functions such as respiration, digestion, glucose metabolism, arousal, regulation of body temperature, blood pressure, swallowing, coughing, sneezing, vomiting, circadian rhythms, etc
specific groups of neurons
- Reticular formation
- Suprachiasmatic nucleus (hypothalamus)
- Ventromedial nucleus (hypothalamus)
reticular formation
A complex network of cells in the core of the brainstem involved in the control of arousal and sleep
SCN
Controls the circadian (24 hr) biological rhythms
ventromedial nucleus
Controls the conversion of blood glucose into body fat
equipotentiality
- Jean Pierre Flourens (1794-1867)
- Flourens was one of the earliest proponents of the idea that cognitive functions (such a memory) are not localised but diffusely distributed in the brain
- Following experiments on animals, he concluded that basic physiological regulation and motor functions (breathing, circulation) are localised (e.g. breathing regulation in the brain stem and control of balance in the cerebellum)
- However he could not localise cognitive functions and concluded that different parts of the brain may be equally involved (equipotential) regarding these functions
phrenology
- School of thought that attempted to localise mental processes anatomically
- Franz Gall (1758- 1828)
perception: hierarchical organisation
- The cortical areas where the sensory information arrives (via relay nuclei in the brainstem, particularly via the Thalamus) are referred to as primary visual/auditory/sensory-motor areas
- This perceptual information then gets passed to the secondary sensory areas, where more sophisticated processing takes place
- From the secondary sensory areas, the processing moves to the association areas, where information from different modalities and of different types is integrated
visual perception: hierarchical organisation
- Visual processing is segregated into: a pathway specialised in the analysis of the stimulus features (colour, shape)- the ‘what’ pathway
- …and a pathway specialised in rapid detection of stimulus location and motion- the ‘where’ pathway
visual processing in the Fusiform gyrus
- ‘What pathway’
- Cells in the inferior temporal lobe (the Fusiform gyrus) seem to respond to highly complex visual stimuli
- There is an area in the Fusiform that seems to specialise in face recognition (Fusiform Face Area, FFA) - recognises faces
- Neuroimaging studies of face processing consistently find FFA activation
- Damage to FFA or cell loss in FFA due to degeneration often result in impaired face recognition- prosopagnosia
motor control: hierarchical organisation
- Around central sulcus
- The control of movement has a similar hierarchical structure
- The primary motor cortex exerts direct control over movement
- However, other areas (premotor - execution of movement, and supplementary motor - planning stages of motor system) are involved in the planning of movement and integration of motor behaviour with other behaviour
- In addition, some sub-cortical structures (Basal Ganglia) and brainstem structures and groups of cells (Cerebellum; Substantia Nigra) are also involved in the fine-grained co-ordination and timing of movements
challenges in functional localisation
- The dorso-lateral prefrontal cortex (dlPFC) is the region of the brain which expanded more than any other in the course evolution of primates…
- Yet patients with lesions to this region rarely show selective/specific deficits
- Based on classic neuropsychological studies, it may seem that localisation of function in the brain is relatively straightforward- and it is just a question of time before the specialisation of all areas is revealed Far from it!
- Take for example Broca’s area and speech production
- It is active in about 10% of brain imaging studies that do not involve linguistic tasks
- Because evidence from brain damage and brain stimulation has shown Broca’s area to be essential for speech production, the above findings could mean that either:
- Broca’s area is not specialised in any specific function, it is active in various tasks
- Only a smaller region within what is traditionally seen as Broca’s area is specialised in speech production (and the exact location of this small sub-region may vary over individuals), but other parts of Broca’s area are not specialised in speech production, or language
where is the control over basic physiological processed performed?
in the phylogenetically old structures of the brainstem
why is little brain space dedicated to important phys processes?
they are ‘hard-wired’ and not subject to plasticity (e.g. learning)
what are higher-order cognitive functions supported by?
both cortical and sub-cortical structures
what do cortical representations show?
hierarchical organisation, with increasingly abstract level of stimulus representation (from primary to secondary sensory areas to association areas in the sensory and motor cortices)
why do primary sensory and motor regions occupy a small area of the cortex?
compared to secondary and association areas - probably because the more complex and flexible (task- and goal-relevant) processing is performed by secondary and association areas
is there localisation of function?
- Some processes show very clear and specific localisation and some brain regions are clearly specialised (e.g. primary sensory and motor areas)
- Some brain regions are clearly more essential for certain processes than other brain areas (e.g. hippocampus for memory)
- Higher cognition (e.g. attention, language, reasoning) may be localised, at least to a degree - but this localisation is more distributed and more variable(probably because they consist of multiple more elementary processes)
- The challenge is therefore to identify the more elementary constituent processes; part of the problem is also that imaging techniques/analyses may be coarse (see example with recent imaging of Broca’s area)
- In addition to brain regions that show at least some degree of specialisation, there also seem to be some rather large multiple demand (general purpose) brain regions
can we use the localisation that does exist?
- Can the anatomical region tell us anything about the psychological process that resides there, or the relationship between that process and behaviour?
- It might - consider the following kind of inference often made in neuroimaging, the reverse inference
- Say you are a psychologist interested in Post-Traumatic Stress Disorder, particularly in the “flashbacks” experienced by individuals with PTSD
- You want to know if the flashbacks are predominantly visual or whether they involve auditory, tactile, olfactory imagery
- If visual, auditory, tactile an olfactory imagery are localised to different brain areas…
- Then imaging someone’s brain while they experience flashbacks may provide you with the answer by comparing the activation of the areas associated with different kinds of imagery
