Brain Basis of Vigilance and Attention: Definitions and ADHD

1. ATTENTION Part 1: Definitions, brain basisIsabelle Rapin Part 2: ADHD Puja Patel Seminar on Developmental Disorders November 6, 2013 No conflict of interest

2. 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)

3. Vigilance vs. Attention • Vigilance: state of arousal of the brain (midbrain RAF) • Attentionto 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 slow-wave sleep • active when no exogeneous stimuli • role in top-down responses to exogeneous stimuli

4. Brainstem maintenance ofvigilance; 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)

5. 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.

6. 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)

7. 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

8. 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)

9. 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

10. 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

11. 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