Effects of parietal TMS on visual attention shifts

Effects of parietal TMS on visual attention shifts Mark Dennison & Ramesh Srinivasan, Ph. D Human Neuroscience Laboratory University of California, Irvine hnl. ss. uci. edu

TALK OVERVIEW ● Attentional control in posterior parietal cortex (PPC) ● Transcranial Magnetic Stimulation (TMS) ● Analyses ● Significance and implications

COVERT SPATIAL ATTENTION – Most attentional shifts are accompanied by shifts in eye, head and bodily orientation (overt attention) – Often need to attend to a stimulus without directly orienting towards it (covert attention) – Visual example: Fighter pilot HUDs – How can we measure this? http: //strikefighterconsultinginc. com/wp-content/uploads/2012/03/url 10. jpg

STIMULUS Rapid Serial Visual Presentation (RSVP) 1 180 frames/trial, 60 Hz refresh rate Left Letter Flicker: 10 Hz Right Letter Flicker: 7. 5 Hz ~1500 ms ~33 ms ~1500 ms 1000 ms 1. Modified version of Sperling et al. , 1980

WHAT BRAIN REGIONS CONTROL ATTENTION? ● ● A network of parietal and frontal regions appears to be responsible for top-down modulations of visual attention 2 Posterior parietal cortex (PPC) acts as the central hub for control of attentional shifts 3 2. Yantis et al. , 2002, 2003 3. Greenberg et al. , 2010 http: //www. livescience. com/7110 -store. html

LATERALITY OF PPC Regions of the left PPC are responsible for maintaining the current attentional state 5 Regions of right PPC are active during shifts of attention to either the left or right side of space 4 4. Yantis et al. , 2002 5. Serences et al. , 2006 http: //www. ning. com/code/wp-content/uploads/2011/04/brain. jpg

HOW CAN WE MODULATE BRAIN NETWORKS? -Transcranial magnetic stimulation (TMS) is a form of noninvasive brain stimulation -TMS induced neuronal depolarization over PPC will likely trigger action potentials across the whole attentional network with time and functionally specific dynamics 6 6. Garcia et al. , 2011 http: //www. berkeley. edu/news 2/2010/09/leftright. jpg

TMS CONFIGURATION Left PPC Right PPC

THE CURRENT STUDY ➢ Can we use cortical stimulation to enhance attentional control? Is there a temporal window in which pulsing is most effective? http: //etc. usf. edu/clipart/33000/33074/clock-03 -20_33074. htm Does hemisphere of stimulation matter?

TMS BY TRIAL CONFIGURATION Trial Start Cue Trial End Subject Response Pulse Time (ms after cue) 0 32 64 96 128 160 192 No TMS

STIMULUS BLOCK INFORMATION One Block = 112 trials 56 left switches 7 trials of each pulse condition 56 right switches 7 trials of each pulse condition Randomized

SUBJECTS ● 4 subjects: two males, two females ● None reported ever having: ● – head trauma – personal or family history of epilepsy – other neurological disorders that might have been affected by the TMS pulse Experiment participation over three separate days – Day 1: One block of training without TMS – Day 2 & 3: Three blocks with TMS over P 1 or P 2 each day

ANALYSES Cue Letter corresponding to response Δ ● ● ● Attention shift times (Δ) averaged across key presses for each subject Data binned according to: – timing of the TMS pulse (0, 32, 64, …, 192, No TMS) – hemisphere of stimulation (Left vs Right PPC) – side of attentional deployment (Left vs Right) Performed an 8 X 2 ANOVA and multiple comparison analysis for each subject

RESULTS Separate Block of no TMS trials collected on another day to compare with interleaved condition F(7, 8) = 4. 16, p <. 0005 F(7, 8) = 2. 92, p =. 0051 SB: F(7, 9) = 10. 35, p <. 0000

RESULTS Main Effect of Stimulation Side by Subject LP RP F(1, 2) = 16. 21, p <. 0005 LP RP F(1, 2) = 22. 17, p <. 0000

RESULTS Main Effect of Shift Side by Subject F(1, 2) = 13. 95, p <. 0005 F(1, 2) = 5. 81, p =. 0163 F(1, 2) = 84. 05, p <. 0000 F(1, 2) = 9. 91, p =. 0017

SUMMARY RESULTS ● ● High pulse timing resolution may not be important for attentional enhancement Right PPC stimulation appears to speed attentional shifts

IMPLICATIONS & FUTURE WORK ● ● ● Individual differences abound in TMS effectiveness Measurement of online neural activity (f. MRI/EEG) during covert attention shifts under influence of parietal stimulation is necessary Successful attentional enhancement through TMS of right PPC may serve useful in: – Post-stroke / traumatic brain injury rehabilitation – Human performance enhancement

THANK YOU! ● UROP ● HNL members ● Dr. Ramesh Srinivasan & Dr. Emily Grossman (UCI) ● Dr. Javier Garcia (UCSD)

QUESTIONS ?