Developmental Neuroscience Methods Flashcards
Why study development?
Give us information about our origins and processes that give rise to us.
In the case of developmental neuroscience we need to consider biology to fully understand the process of development
What is the process of prenatal structural development?
The process of brain development is quite staggering in terms of the complexity and numbers of cells which it involves
Human adult brain =
~100,000,000,000 neurons (number of trees in Amazonian rainforest (1/4 number of trees in the world)
~60,000,000,000,000 synapses (number of leaves in Amazonian rainforest)
Many of these neurons are created during prenatal brain development
The neural tube to the nervous system
Once the zygote implants in the uterine wall it becomes a flat disc of cells with 3 layers (endoderm, mesoderm, ectoderm)
At about 24 days a portion of the ectoderm folds in on itself to become the neural tube
As early as 5 weeks post-conception) the neural tube develops subdivisions along its:
Length
Circumference
Radial dimension
These subdivisions provide specialisation of function and are seen in cellular differentiation
Differentiation in the neural tube
Length (in bulges) telencephalon (cortex) diencephalon (thalamus, h-thalamus) mesencephalon (midbrain) metencephalon (cerebellum) myelencephalon (medulla) 2) Circumference -The dorsal side of the tube gives rise to sensory areas whereas the ventral side of the tube gives rise to motor areas 3) Radial dimension -Along the radial dimension the cells differentiate into the separate layers found in the adult brain
Changes on neural level during brain development
Cellular differentiation of nervous system is largely complete at birth
Disagreement about whether large numbers of new cells are created postnatally
Main changes are:
Proliferation of synapses, and synaptic pruning and cell death (“rise and fall”)
Myelination
There is a reduction in grey matter across the brain into adolescence -thought to represent synaptic pruning
Structure development
Some parts of the brain develop slower than others
Huttenlocher (1990) – frontal areas much slower to develop anatomically than parietal and occipital
Interestingly, the frontal lobes (neocortex) are the most recently evolved area of the brain and are substantially larger in humans compared to any other animal, relative to brain size
Cortical specialisation during development
Functional specialisation of cortical areas continues to change right across childhood, e.g.:
Several fMRI studies (e.g., Golarai et a., 2007; Scherf et al., 2007) now show that the brain areas involved in face processing continue to develop into adolescence
) more and/or less brain regions become involved with age
2) more specialisation of particular areas to face processing with age
What are some research methods in developmental cognitive neuroscience
Marker tasks
Tasks which we know are subserved by specific brain regions/networks in adults
Imaging methods
Methods for examining brain processes during tasks
Computational modelling
Explicit theories of how development takes place on a neural level
What are marker tasks?
Behavioural tasks which we know are subserved by specific brain regions/networks in adults
Improvements/developments at the task may reflect changes in the functionality of the underlying brain structures
Particularly useful given that it is often difficult to use imaging methods with infants
Examples
- Perceptual markers of cortical function (orientation, pattern perception)
- Visual orienting markers of cortical function
- Behavioural markers of prefrontal cortical function
perceptual markers of cognitive function
Bronson (1974, 1982)
Introduced the argument that developments in visual perception and orienting were underpinned by maturation of cortex
Bronson argued at early perceptual abilities in newborns were subserved by subcortical structures (esp. Superior Colliculus)
Markers:
Orientation discrimination: Argued to be subserved by orientation sensitive neurons in primary visual cortex; V1 (no orientation sensitivity has been observed in SC)
Pattern discrimination: Pattern sensitivity is shown in early visual areas of cortex; V1, V2 etc.. (only some very simple socially relevant visual patterns are thought to be encoded in SC – cf. Johnson et al..)
Imaging methods in developmental cognitive neuroscience
Methods for examining brain processes during tasks
A wide range of imaging methods have been used with young babies and children including fMRI, MEG, EEG/ERP, & fNIRS
EEG in infants
Investigations of both ERPs and oscillations in the EEG
As with adults: low spatial res., but great temporal res.
Differences with adult EEG:
Difficult to collect as many trials
Difficult to control movement artefacts
->often simpler experiments (fewer conditions)
->Problems with trial numbers and artefacts are, to some extent, offset, by the larger amplitude ERPs seen in infants (higher signal to noise due to thinner skulls and less hair etc.)
Often use the more expensive EGI system as it is quicker to apply and does not involve abrasion and gel
Limitations of imaging methods in infants
Although fMRI is routinely used with children from 6 years of age up, the difficulty of using it with younger children has restricted its use to a handful of non-clinical studies:
The crucial problem is that fMRI / PET / MEG require the participant to be very still; in addition, PET requires injection of radioactive isotopes
There are also a few MEG studies (all with sleeping infants (so typically investigating auditory and somatosensory processing)
Functional near infrared spectroscopy (fNIRS)
fMRI for infancy researchers (see Lloyd-Fox et al., 2010)
Measures blood oxygenation via infrared light
Bone and tissue are quite transparent to infrared light
Yet haemoglobin (oxy- and deoxy-haemoglobin) absorbs infrared light
Amount of light which makes it back to the detectiors used to calculate the amount of oxygenated blood (gives BOLD response)
Not as spatially precise as fMRI, but much less invasive and resilient to movement (unlike fMRI and EEG)
Computational methods in infants
It is very difficult to observe development in the brain directly (would require exhaustive longitudinal methods)
An important tool in this regard is computational modelling
–>Theories and predictions about how developmental changes in the biology of information processing might occur, e.g.,
1) The way the models are structured (their architecture) can be thought of as modelling genetic predisposition
2) The way they learn from the structure of their sensory input can be thought of as the influence of the environment
