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Part 1: Definitions, brain basis Isabelle Rapin

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1 Part 1: Definitions, brain basis Isabelle Rapin
ATTENTION Part 1: Definitions, brain basis Isabelle Rapin Part 2: ADHD Puja Patel Seminar on Developmental Disorders November 6, 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) 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 slow-wave sleep active when no exogeneous stimuli role in top-down responses to exogeneous stimuli

4 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)

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

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