The effects of electrical microstimulation on cortical signal propagation Nikos K Logothetis, Mark Augath, Yusuke Murayama nature neuroscience: 5 September

Glossary Functional Magnetic Imaging (fMRI) Blood Oxygen Level-Dependent (BOLD) Positive/Negetive BOLD responses (PBRs/NBRs) Thalamic region: – Lateral Geniculate Neucleus (LGN) – Superior Colliculus (SC) – Pulvinar (PUL) Primary visual cortex (v1) Extrastriate cortex: – Secondary visual cortex (v2) – XC that refers to V3, V3A, V4, V4T, posterir TEO – MT (v5) 2

Results  Electrical stimulation disrupts cortico-cortical signal propagation by silencing the output of any neocortical area whose afferents are electrically stimulated. Scientific Basis: Stimulation of a site in the LGN increased the fMRI signal in the regions of V1 that received input from that site, but suppressed it in the retinotopically matched regions of extrastriate cortex. A short excitatory response occurring immediately after a stimulation pulse was followed by a long-lasting inhibition. 3

a)t static maps for LGN stimulation. b)Time course of the BOLD fMRI responses in different visual structures during LGN stimulation. c)t statistic maps for pulvinar stimulation. d)Time course of the BOLD fMRI responses in different visual structures during pulvinar stimulation. 4

Combined visual and electrical stimulation of the LGN a) t statistic maps, b) Time course of the BOLD fMRI responses, c) Average BOLD responses. 5

Effects of stimulation frequency on the BOLD responses a) Upper traces show typical V1 (red, positive) and V2 (blue, negative) responses during LGN stimulation. Inset shows activeted (V1, red) and deactivated (V2, bluse) areas. b)Combined visual and electrical stimulation at 12Hz. c)BOLD responses in areas V1 and V2 for visual and electrical stimulation at different frequencies. 6

Neural responses to single electrical pulses a)Raster plots and peristimulus histograms. b)PCA c)K-means clustering. d)C1-3 clusters powers. e)Electrode depth of the recorded sites of each cluster. f)Pulse efficiency. g)Inter-pulse spiking activity. 7

Conclusion The authors found that electrical stimulation of a thalamic site suppressed the neural activity of its projection regions in visual cortex. The magnitude of the suppression depended on stimulation frequency. This effect was independent of current strength. Intracrotical recordings in V1 showed that an electric pulse typically evoked an action potential followed by a pronounced and long-lasting inhibition. Stimulation of LGN consistently activated superior colliculus and pulvinar, even though neither structure receives direct LGN input. 8

Strong claim in the paper! “We propose that many of the behavioral effects that have been observed over the years following electrical stimulation of the afferents of sensory or association cortical areas are in fact largely mediated by cortico- subcortico-cortical pathways.” Corresponding author: Nikos K Logothetis Max Planck Institute for Biological Cybernetics, Tubingen, Germany. 9