Neuroimaging and Autism Dr Matt Roser Lecturer, School of
Psychology Plymouth University [email protected]
What are the techniques? What are the coloured blobs in an fMRI
report? How do we conduct research with autistic people? What are
the major findings and areas of current research? How can this
help?
Historical Images of the Brain and Mind Brain structure Some
still in use today Often Interpretive, labour/skill intensive.
Brodmann cytoarchitecture mapsChristopher Wren (1664)
Electrophysiological mapping (1957)Phrenology (19thC)
Historical Images of the Brain and Mind Brain function
What do those blobs represent?
Magnetic Resonance Imaging (MRI) Physics Uses a magnetic field
and radio energy to produce an image A large magnet (50,000 x
Earth) aligns nuclei that have a net magnetic moment Nuclei absorb
and re-emit radio frequency energy
Functional MRI (fMRI) The Blood Oxygen Level Dependent (BOLD)
Response Relative levels of de/oxyhaemoglobin change from regional
cortical activity Regional blood oxygenation actually increases
following neural activation. Local field strength is affected by
relative levels This affects the local signal in the image.
Increased signal is obtained from active regions
The fMRI environment
A simple experimental design Task and Rest conditions can be
compared The difference in signal between the conditions is tested
at each of thousands of voxels The significant statistics are
coloured the blobs show areas of significant condition effects Time
Task Rest Task + +
Build Model Realignment & motion correction Smoothing
Normalisation Image Data Parameter EstimationAnatomical Reference
Kernel Data Design Matrix Statistical Parametric Mapping Contrasts
fMRI Preprocessing and Analysis - its complicated!!!
Blobs are clusters of significant statistics for either a main
effect or a contrast between two sets of regressors at each voxel
Shows areas where the signal change was significantly predicted by
the model (or where the degree of prediction differed between
contrasted conditions) This is the end result after much
preprocessing and analysis Change in the signal is due to regional
hemodynamics Thus, activations are distantly related to the
underlying neurological events
Diffusion Tensor Imaging (DTI) A structural imaging technique
probe tissue microstructure using water diffusion Water molecules
in the brain are mobile Diffusion in three dimensions can be
assessed by applying magnetic gradients This can tell us about
brain structural connectivity
Challenges faced when running a brain-imaging study of
autism
Major findings: Brain regional volume Brain structural
connectivity Brain functional connectivity and functional
reorganisation
Gross brain volume Early increase Grey and white matter
Particularly frontal regions (DLPFC, MPFC) Longitudinal studies
needed Failure of synaptic pruning, or an excess of synaptogenesis?
Amaral, Schumann, & Nordahl (2008). Neuroanatomy of autism.
Trends in neurosciences, 31(3), 137-145.
Regional brain volume Numerous widespread areas implicated
Cerebellum - Mixed evidence for enlargement - Depends on regional
definition - Some evidence for enlargement beyond that of cortex A
small number of histological studies suggest decreased cell density
in autism Cohort differences histology/MRI? Amaral, Schumann, &
Nordahl (2008). Neuroanatomy of autism. Trends in neurosciences,
31(3), 137-145.
Regional brain volume Amygdala involved in memory, emotion
(fear), learning Early enlargement (8-12), lack of preadolescent
increase in volume Many conflicting histological findings Basal
ganglia (particularly caudate) Increased size repetitive behaviours
Amaral, Schumann, & Nordahl (2008). Neuroanatomy of autism.
Trends in neurosciences, 31(3), 137-145.
Brain structural connectivity An example study: Frontal lobe
tracts and the corpus callosum show alterations in diffusion or
geometric properties (ASD lower fractional anisotropy) Inclusion
criteria for the ASD group (N=32, 5-9 yrs): 1) diagnosis of
Autistic Disorder, Aspergers Disorder, or Pervasive Developmental
Disorder 2) scores above the cutoff on the Social Communication
Questionnaire and Autism Quotient (AQ) Review (Travers, 2013) found
generally lower tract integrity in ASD throughout corpus callosum,
cingulum and left-temporal lobe Kumar, et al. (2010). Alterations
in frontal lobe tracts and corpus callosum in young children with
autism spectrum disorder. Cerebral cortex, 20(9), 2103-2113.
Brain functional reorganisation Many task-specific examples of
anomalies, such as reduced amygdala activation during a mentalising
task (Reading the Mind in the Eyes) (Baron-Cohen etal., 1999) add
to this - language comprehension, working memory, face recognition,
and eye movements Trawling through a great number of studies, with
different tasks and participants is bewildering Control, Autistic,
Both Autistic less activation of left-temporal regions
Brain functional reorganisation Meta-analyses can bring sense
to the data General pattern: More diffuse network of regions in ASD
Diminished activity in task-related regions and increased activity
in task-unrelated regions Philip, R., Dauvermann, M. R., Whalley,
H. C., Baynham, K., Lawrie, S. M., & Stanfield, A. C. (2012). A
systematic review and meta-analysis of the fMRI investigation of
autism spectrum disorders. Neuroscience & Biobehavioral
Reviews, 36(2), 901-942. Social tasks reduced fusiform activation
in face perception and interpretation of expressions Increased
activity in temporal lobe Executive tasks Reduced activation in
dorsolateral prefrontal cortex, inferior parietal lobe, insula, and
posterior cingulate gyrus, areas associated with inhibitory control
and attentional orienting Increased activity in posterior visual
areas (visual imagery strategy?)
Brain functional connectivity Brain function comprises networks
of active regions (such as Brocas and Wernickes language areas)
Activity in these dispersed regions correlates functional
connectivity Underconnectivity theory of autism postulates that
individuals with autism have a reduced communication bandwidth
between frontal and posterior cortical areas Here the ASD group (17
adults) showed more activation than the control group in Wernickes
area and less activation than controls in Brocas area Functional
connectivity was reduced in ASD Just, M. A., Cherkassky, V. L.,
Keller, T. A., & Minshew, N. J. (2004). Cortical activation and
synchronization during sentence comprehension in high-functioning
autism: evidence of underconnectivity. Brain, 127(8),
1811-1821.
Electroencephalography (EEG) and event-related potentials
(ERPs) Relatively non-invasive More clinically available Passive
recordings of brain electrical activity Can measure global/regional
brain state or processing of specific stimuli Excellent temporal
resolution relatively poor spatial resolution
Electroencephalography (EEG) and event-related potentials
(ERPs) Oscillatory activity in different bandwidths can be used to
index functional connectivity General pattern - abnormal functional
connectivity between frontal and posterior regions and enhanced
power in the left hemisphere in ASD Local overconnectivity, global
underconnectivity
Electroencephalography (EEG) and event-related potentials
(ERPs) An ERP example: (Frey et al., 2013) Anomalies in fixation.
Manifest in brain sensory electrical response? Peripheral visual
stimuli. Sensory ERPs compared (Group N = 22 ASD; 7-17 yrs)
Processing of lateralized visual stimuli is different in children
and adolescents with ASD compared with age-matched controls.
Reflects altered cortical representations of visual space in ASD?
Consequence of the more variable fixation behaviour?
How can these techniques help? Brain anatomy as a biomarker for
autism (Murphy, et al., 2011) - Identify ASD sample with 85%
accuracy using automated analysis of brain anatomy Aiding dignosis?
- Targeting support? Good or bad?
How can these techniques help? Measure the effects of
interventions - 100 hours of remedial reading training eliminated
regional white- matter integrity differences between poor-good
readers - Changes suggest myelination Keller TA, Just MA. Altering
cortical connectivity: remediation-induced changes in the white
matter of poor readers . Neuron. 2009, 10;64(5):624-31.
Future directions Integration of technologies Models of
functional connectivity informed by brain structure Temporal and
spatial aspects united Larger studies (N = hundreds, not tens)
Longitudinal, rather than cross-sectional, designs to address
complex developmental trajectories Distinct phenotype subject
groups Extension of studies into the adult brain Majority of those
with the disorder Freedom from developmental confound may yield
novel insights
Finding out more Google Scholar
Finding out more Free access to peer-reviewed science
http://explore.tandfonline.com/page/beh/world-autism-day-2014/
Finding out more open-access journals
END
HEIGHT COLOUR WIDTH Our fMRI experiment on Relational
Integration Participants Aspergers Controls N 13 (2 Female) 13 (3
Female) Age (x, sd) 37 (11) 35 (9) IQ (x, sd) 112 (17) 135
(34)
Our fMRI experiment on Relational Integration Asperger >
Control Task v Baseline Middle occipital gyrus, precuneus (BA19)
Visuospatial tasks; Empathy; Perspective taking; Motor
planning
Diffusion-Tensor Image data Group differences in FA Aspergers
> Control Control > Aspergers Our fMRI experiment on
Relational Integration