Y Cognitive Enhancement with Transcranial P O Direct Current Stimulation (tDCS) C T O N O D E S A E David Fischer L Berenson-Allen Center for Noninvasive Brain P Stimulation, BIDMC Harvard Medical School
Y P Neuroenhancement O C T O N The enhancement of normal brain processes in O D healthy individuals E S A E L P
Y P Cognitive Enhancement with tDCS O C T Memory Executive functions • • O Set-shifting Digit-span recall – – Stop signal tasks Verbal episodic – – N memory Stroop tasks – Visual working Language – • memory O Grammatical – N-back working learning – memory Lexical learning D – Mental arithmetic • Verbal fluency – Automaticity • Naming – E Picture viewing/rating • Attention • Visual perception • Selective attention S – Multimodal perception • Spatial attention – A Social cognition • Learning • Problem-solving • Motor learning E – Mood • Procedural – Gambling based risk- Santarnecchi et al. 2015 learning L • taking Explicit learning – P Rumination • Numerical learning – Coffman et al., 2014; Horvath et al., 2015
Y P Cognitive Skills O C T • Learning O – Implicit N • Motor/procedural • Probabilistic O – Explicit D • Working Memory E • Attention S • Social Cognition A E • Language L • Complex Problem-Solving P
Y P O C T O N O D E S A E L P
Y P O C T O N O D E S A E L P
Y P O C T O N O D E S A E L P
Y P O C T O N O D E S A E L P
Y P Enhancement of Implicit Learning: O Procedural/Motor C T tDCS of the left primary O motor cortex enhances motor N learning of the contralateral hand (Nitsche et al., 2003) O tDCS of the primary D motor cortex decreases motor E learning of the contralateral hand S (Vines et al., 2006) A tDCS enhances motor E learning of the ipsilateral hand L P
Y P Enhancement of Implicit Learning: O Procedural/Motor C • Learning occurs in 3 stages T O – Acquisition Consolidation Retention N • tDCS improves motor learning by enhancing consolidation (Reis et al., 2009) O D E S A E L • Others have shown additional improvements in P retention (Galea & Celnik, 2009)
Y P Enhancement of Implicit Learning: O Probabilistic C T • Probabilistic Classification Learning Task O (Kincses et al., 2003) N O D E S A E L P
Y P Enhancement of Implicit Learning: O Probabilistic C T tDCS of the left O dorsolateral prefrontal cortex N (DLPFC) enhances probabilistic learning (Kincses et al., 2003) O D E S A E L P
Y P Enhancement of Explicit Learning O C Enhancement of explicit learning consolidation T • during sleep (Marshall et al., 2004) O – List of words presented to subjects N tDCS of bilateral DLPFC during slow wave sleep O – Enhanced recall of words D E S A E tDCS of right temporoparietal area L enhances memory of object locations after a 1 week delay (Flöel et al., 2012) P – However, no difference in immediate acquisition
Y P O Physiology of Learning Enhancement C • Clark et al. found T tNAA improvement in spatial O learning with tDCS N to right parietal cortex (2012) O • They then use magnetic D resonance spectroscopy to measure metabolites under Glx E anode (2011) S • Elevations in: A – Glutamine/glutamate (Glx) E – N-acetylaspartate/N- L acetylaspartylglutamate P (tNAA)
Y P O Physiology of Learning Enhancement C • Glx T – Glutamate (Glu) is major excitatory O neurotransmitter N – Metabolized to glutamine (Gln) – Glutamate binds to NMDA receptor O for excitation, long-term potentiation D – NMDA antagonists suppress tDCS effects, while NMDA agonists enhance tDCS effects (Clark et al., 2011) E • tNAA S http://www.cnsspectrums.com/userdocs/ArticleImages/1105cns.acsupp02.gif – Thought to be related to neuronal A energy status E – May be due to increased metabolic L activity from increased glutamatergic activity P
Y P Enhancement of Working Memory O C T • The N-back working memory task (Fregni et O al., 2005) N O D E S A E L P
Y P Enhancement of Working Memory O C tDCS of left DLPFC enhances T performance on 3-back working O memory task (Fregni et al., 2005) N O D E tDCS of the left DLPFC, S combined with N-back working A memory task, enhances later E performance (Andrews et al., 2011) L – Neither tDCS nor N-back testing alone P was sufficient
Y P Physiology of Working Memory O Enhancement C T (compared to ) tDCS of the left O DLPFC during a 2-back working memory task N (Zaehle et al., 2011): O – Enhanced working memory D – Increased alpha and theta frequencies E • Alpha and theta frequencies have been linked to S working memory (Klimesch et al., 2005) A – Alpha thought to inhibit non-task relevant areas E – Theta associated with memory encoding and retrieval L P
Y P Enhancement of Attention O C T • Executive Attention: Sternberg task (Gladwin et O al., 2012) N O D E S A E L P Interference level: High Low High
Y P Enhancement of Attention O C T tDCS of the left DLPFC O improved reaction time on N only on high-interference O probes (Gladwin et al., 2012) D E S A E L P
Y P Enhancement of Attention O C T • Visual Vigilance Task: Air Traffic Control O (Nelson et al., 2014) N O D E S A E L P
Y P Enhancement of Attention O C • With sham tDCS, attention T decreases over time (Nelson et al., O 2014) N – Lower target detection rate O – Slower reaction times – Reduction in cerebral blood flow D velocity E tDCS of the DLPFC (either S left or right, left > right) enhances A attention E – Higher target detection rate L – Maintained blood flow velocity P – Increased cerebral oxygenation
Y P Enhancement of Attention O C T • Spatially-Specific Attention Task (Sparing et al., O 2009) N O D E S A E L P
Y P Enhancement of Attention O C T O N O D E S A E L P Blumenfeld, 2010
Y P Enhancement of Attention O C • Visual detection in half of the T visual field is enhanced by O tDCS of the contralateral parietal N cortex (Sparing et al., 2009) O D E S A E L P • Or by tDCS of ipsilateral parietal cortex
Y P Enhancement of Social Cognition O C Subjects quickly shown a series of happy, T • sad, or neutral faces O ✚ Asked to identify either happy or sad • faces N tDCS of the left temporal cortex & tDCS of the right temporal O cortex enhances recognition of sad faces D – … only in women – Impairs recognition of sad faces in men E S A E L P
Y P Enhancement of Language O C T tDCS of Broca’s area O enhances grammatical N learning (de Vries et al., 2009) O D tDCS of Wernicke’s E area enhances lexical learning S (Flöel et al., 2008) A E L P
Y P Enhancment of Complex Cognition O C Remote associates test (Cerruti & T • Schlaug, 2009) O – Given 3 words, have to find a word N associated with all 3 – E.g., “Child, Scan, Wash” O – Answer: “Brain” D tDCS of the left DLPFC enhances performance E S A E L P
Y P Mood enhancement O C • Observed that tDCS can T induce mood changes O in healthy subjects N • Marshall et al. (2004) found improvement in O mood with anodal tDCS D of bilateral DLPFC • However, recent E placebo-controlled S studies have found no http://www.thync.com/ A mood changes with tDCS, with various E positions and polarity L (Plazier et al., 2012) P http://icdn4.digitaltrends.com/image/thync_6214-1500x1000.jpg
Y P Cognitive Enhancement with tDCS O C T O N O D E S A E + x L P Santarnecchi et al. 2015
Y P Cognitive Enhancement with tDCS: O Stimulation Sites C T Motor Learning O Attention N Probabalistic Social Cognition O Learning D Explicit Learning Language E S Working Complex A Memory Cognition E L P
Y P Cognitive Enhancement with tDCS: O Stimulation Sites C T Stimulation Sites: Left DLPFC: O N O D E S Left DLPFC A E L P Santarnecchi et al. 2015
Y P Different Functions? O C T O N O • Brain region may be D versatile, supporting E several distinct functions S A E L P
Y P Different Networks? O C T • Stimulation site targets O different networks N • tDCS can alter O functional connectivity D between brain regions E (Coffman et al., 2014), S as demonstrated with A fMRI and EEG E L P
Y P Overlapping Cognitive Skills? O C T • Enhancement of explicit learning with tDCS O correlates with enhancement of attention N (Coffman et al., 2012) O • Enhancement of working memory with tDCS D mediated by enhancement of selective attention (Gladwin et al., 2012) E S • Learning (memory acquisition/consolidation) A linked to working memory and attention E (Coffman et al., 2014) L P
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