The effects of TMS over PPC in a visual feature memory / saccade task

Abstract

Introduction: Perception and action are often treated separately, but ultimately perception must be used to guide meaningful actions when object selection and memory are required. We investigated the role of parietal cortex areas known to be involved in saccade and reach planning (the midposterior intraparietal sulcus [mIPS] and the superior parietal-occipital cortex [SPOC], see Vesia et at. J. Neurosci., 2010) in a delayed match-to-sample saccade task, based on single or multiple visual features. Methods: 4 Head-fixed subjects were shown a ‘probe’ template with a conjunction of two features (shape and texture) at central fixation for 500 ms, and instructed to remember the shape, texture, or both features before each trial. After a delay, subjects were presented with a mask followed by stimuli in four eccentric quadrants for 1 second. Afterwords, subjects were required to saccade to the location of the stimulus that matched the remembered probe. Task difficulty was set during preliminary psyhophysical experiments. Eye movements were tracked using an Eyelink II. During the delay period after the presentation of the probe, 3 TMS pulses (10Hz) were delivered to right mIPS (thought to be involved in both saccades and reach), right SPOC (thought to be involved in just reach), or Cz (control site), run in blocks randomly intermingled with no-TMS trials. Results: For each TMS site, we analyzed subject performance (ability to saccade to the correct object) with a 3(feature condition)x2(visual field)x2(TMS/no TMS)x6(subjects) mixed-model ANOVA, with subjects as a random factor. There was a significant main effect of TMS in the right mIPS condition, but not in the right SPOC or Cz conditions. Conclusion: TMS to the right mIPS (but not right SPOC) disrupted non-spatial feature memory in a match-to-sample saccade task. This may implicate mIPS in an effector-specific network that coordinates feature memory with the planning of action.

Meeting abstract presented at VSS 2012