1 / 20

Inhibitory neural activity produces a significant BOLD response in human cortical areas

Inhibitory neural activity produces a significant BOLD response in human cortical areas. Archana Purushotham, Seong-Gi Kim Center for Magnetic Resonance Research, Depts of Radiology and Biomedical Engineering, University of Minnesota, USA. Acknowledgements:

manchu
Download Presentation

Inhibitory neural activity produces a significant BOLD response in human cortical areas

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Inhibitory neural activity produces a significant BOLD response in human cortical areas Archana Purushotham, Seong-Gi Kim Center for Magnetic Resonance Research, Depts of Radiology and Biomedical Engineering, University of Minnesota, USA Acknowledgements: Robert Jech, Tommy Vaughan, Gregor Adriany, Peter Andersen

  2. Introduction Understanding the neural correlates of BOLD activity: Does it result from excitation alone, or from both excitation and inhibition? Arthurs and Boniface, Trends in Neurosciences 2002

  3. Waldvogel et. al., Nature 2000 Task: simple push-button; go/no-go trials Confirmed inhibition in primary motor cortex (M1) by TMS fMRI: no significant change from baseline for M1 during no-go task; present in pre-supplementary motor area. Inhibition is metabolically much less demanding than excitation: does not give rise to an observable BOLD response in M1. Our hypothesis: Being a very simple task, the inhibitory component accompanying no-go trials is very small, insufficient to give rise to a detectable BOLD response in M1

  4. Objective To determine the BOLD correlates of inhibitory neural activity in the human motor cortex, using a delayed, pre-cued directed go/no-go task.

  5. Paradigm A delayed, cued joystick go/no-go task: • Variable, pseudo-randomized delay periods : 0, 2, 4 and 7 sec • No-go trials occurred 20% of the time: after 7.3 seconds, centre circle turned black instead of green • Trial epochs : 30 or 35 seconds long; 30-40 trials

  6. Data Acquisition fMRI • Single-shot 64 x 64 EPI images using a 4 Tesla MRI system • 9 normal adult, right-handed human subjects • 5 axial sections of thickness 5 mm each, including the primary, supplementary (SMA) and pre-motor areas • TR = 1sec for most subjects; 0.5 sec for 2 subjects • Structural images 128 x 128 T1-weighted (FLASH or segmented EPI) Electromyography • Surface EMG of flexors and extensors of forearm, simultaneously for 3 subjects, pre-fMRI training for 1.

  7. Data Analysis • EMG epochs checked for untimely activity, and behavioural data for errors; corresponding epochs excluded • Timecourses detrended linearly if drifts were apparent • fMRI epochs grouped by delay period and averaged to get mean timecourse for each delay condition • Cross-correlation based on the no-delay epoch time-course used to generate maps (3 maps based on different thresholds)

  8. Data Analysis (contd.) • Primary and supplementary motor areas demarcated manually using structural images • Epoch time-courses created by averaging over activated voxels in each area • Compared time-courses for 7-second delay condition (go) versus no-go condition, for each area • Used data from subjects with sufficient SNR (judging from comparability of preparation activity for go and no-go tasks)

  9. Reaction time (msec) 0 2 4 7 Delay period (sec) Does a state of preparedness to move exist?

  10. Go trial No-go trial Time (sec) Surface electromyogram of forearm muscles

  11. P SMA M1 L R Central sulcus A Contra. Regions of interest Activation map based on no-delay movement

  12. BOLD % change Time (sec) SMA (n = 7; CC = 0.7) Prep. Go/ No-go

  13. BOLD % change Time (sec) M1 (n = 7; CC = 0.7) Prep. Go/ No-go

  14. Consistency of observed result Three statistical thresholds (CC = 0.6, 0.7, 0.8) used for analysis : result independent of threshold • Across subjects: • 6 out of 7 subjects clear inhibition-related BOLD response in M1 • 1 subject amplitude change very low; not individually convincing

  15. Go cue No-go cue Prep. cue Schematic of neural activity Higher order motor areas (including SMA) Primary motor area Muscular activity

  16. Evoked potential recording: preliminary data A Contra. Ipsi. P

  17. Cz (midline) go Evoked potential (V) no-go Time w.r.t appearance of go/no-go cue (100 msec)

  18. C3 (contralateral) go Evoked potential (V) no-go Time (100 msec)

  19. Conclusion Inhibitory synaptic activity in the primary motor area during non-performance of a prepared task is associated with a significant BOLD signal. The amplitude of the BOLD signal peak due to inhibition is comparable to that due to preparation.

  20. C4 (ipsilateral) Evoked potential (V) Time (100 msec)

More Related