Tonotopy during a Change Detection Task: A Multi-Voxel Pattern Analysis Approach Annika Linke MRC Cognition and Brain Sciences Unit MVPA Day October 2009

Investigating Tonotopy Tonotopy: low- to high frequency spatial gradient in anterolateral to posteromedial direction: Aims: Assessing tonotopy using fMRI: possible but difficult due to low SNR substantial inter-individual anatomical differences Maintenance of auditory information? frequency specific sustained firing in auditory cortex?

Task & Stimuli Trial = sequence of two sounds – maintenance – sequence repeated Task = same/different judgement 16 different pure tones (175 – 2794Hz) Four frequency ranges comprising four tones each Maintenance and ITI jittered (2/10s)

Methods high-resolution protocol (32 slices, TR=2150ms, 2.4x2.4x2.4mm) continuous scanning including temporal and parietal cortex, sensorimotor regions, and parts of ventrolateral prefrontal cortex 20 participants (12 completed two sessions) 3 blocks, 8 subblocks

Univariate Analysis FDR corrected at p<0.05 Encoding Maintenance Response FDR corrected at p<0.05 Activation Deactivation

Univariate Analysis – Tonotopy FWE corrected at p<0.005 encoding

MVPA Analysis Correlation of patterns of activity across the four frequency ranges and stages of the STM task by extracting voxel-wise data from each ROI unsmoothed data Six ROIs (superior temporal region representing auditory cortex, planum temporale, Heschel’s Gyrus, intraparietal sulcus (infIPS, supIPS, MD IPS)) Design Issues: grouping of subblocks

Encoding – Auditory Cortex ROI MVPA Analysis Encoding – Auditory Cortex ROI F1 F2 F3 F4 F1 F2 F3 F4

MVPA Analysis Auditory Cortex Heschel’s Gyrus Superior IPS “MD” IPS Encoding Maint. Encoding Maint. Superior IPS “MD” IPS Encoding Maint. Adjust figure (no explanation, exchange left and right …)

Summary Auditory cortex showed strong tonotopic organisation during the encoding phase of a change detection task While sounds are maintained in short-term memory auditory cortex shows frequency specific suppression Posterior parietal regions are involved in the encoding phase of ASTM