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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) • • • • 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 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., ↓ response inhibition → impulsive ↓ sustained attention → distractible ↓ working memory → forgetful ↓ input inhibition and response monitoring ↓ awareness of affective signals & environmental rewards