Transcript ADHD - Albert Einstein College of Medicine

ATTENTION
Part 1: Definitions, brain basis
Isabelle Rapin
Part 2: ADHD
Puja Patel
Seminar on Developmental Disorders
November 6, 2013
No conflict of interest
Connectivity networks
• Defined functionally by
 synchronous/coherent EEG rythmicity in
distant neuronal areas
 synchronous blood oxygen level dependent
(BOLD) activation on fMRI
• Defined anatomically by MRI visualization
of myelinated pathways with diffusion
tensor imaging (DTI)
Vigilance vs. Attention
• Vigilance: state of arousal of the brain (midbrain RAF)
• Attention to exogeneous stimuli: 2 major networks
 Bottom-up = automatic orientation/response to salient sensory
stimuli
 Top-down = choice of response to sensory stimuli given on-going
organismic priorities
• Attention to endogeneous stimuli: default network
(active both awake and in REM sleep; inactive in slowwave sleep
 active when no exogeneous stimuli
 role in top-down responses to exogeneous stimuli
Brainstem maintenance of
vigilance; arousal
• Ascending pathways from pons/midbrain (RAF)
→ intralaminar nuclei of thalamus → forebrain
 Control (with diencephalin nucleip) of wake/sleep cycle
 Noradrenergic inputs from locus coeruleus → wakefulness + REM
sleep
 Cholinergic from pons → slow wave sleep
• Receives sensory inputs (somatosensory, visual,
& auditory especially → thalamo/1o cortices)
 Orientation (forced attention) to sensory input
 Saccadic eye movements (superior colliculus → frontal eye
fields)
Attention - Definition
• Presupposes vigilance
• Ability to make choices for action among a
myriad of competing stimuli in order to
match task demands by
• Enhancement of attended stimuli
• Suppression of unattended stimuli
• Requires executive skills (prioritize, etc.)
•
“
working memory
•
“
etc.
Control of attention
• Exogenous (reflexive bottom-up – conscious
awareness not required, imperative)
• Endogenous (cortical, top-down choices to
match on-going needs)
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Monitor & maintain goal directed activities
Deactivate inappropriate tasks
Prepare activation of relevant tasks
Modulated by on-going affective signals (role of
anterior cingulate cortex)
Bottom-up attention network
• Selection of sensory saliency: (right)
lateral intraparietal cortex – disengage
from current target
• Orient focus of attention: superior
colliculus
• Engage to new target, i.e., synchronize
relevant cortical areas: pulvinar
• [Enhance vigilance: RAF]
Posner 2012, Miller & Buschman 2013
Top-down attention network
(goal-directed action)
• Prefronto-parietal dorsal connectivity
• Widespread cortical to subcortical areas
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Lateral prefrontal - working memory, executive
Anterior cingulate - interface cognition & emotion
Diencephalic nuclei
Etc.
• Multimodal intraparietal/temporo-parietal
association cortical areas (right dominant
> left)
Default mode network
• Networks active/enhanced in the absence
of exogeneous stimuli
• Not “rest” but basis for continuous
endogenous brain activity
• Persists in sleep (except slow wave) and
even under anesthesia
• Associated with rapid (gamma, beta) EEG
anteriorly, alpha (eyes closed) oscillations
posteriorly
M. Raichle
The restless brain
Brain connectivity 2011;
1: 3-12
fMRI BOLD coherence in
spatial networks
activated by consecutive
task evoked responses in
a single subject
ADHD
• Bottom-up attention: spared
• Default network: data presumed impaired
• Top-down attention: multiply impaired, e.g.,
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↓ response inhibition → impulsive
↓ sustained attention → distractible
↓ working memory → forgetful
↓ input inhibition and response monitoring
↓ awareness of affective signals &
environmental rewards