Efficient neural processing depends on regulating responses through suppression and facilitation of neural activity. Utilizing a well-known visual motion paradigm that evokes behavioral suppression and facilitation, and combining five different methodologies (behavioral psychophysics, computational modeling, functional MRI, pharmacology, and magnetic resonance spectroscopy), we provide evidence that challenges commonly held assumptions about the neural processes underlying suppression and facilitation. We show that: (1) both suppression and facilitation can emerge from a single, computational principle-divisive normalization; there is no need to invoke separate neural mechanisms, (2) neural suppression and facilitation in the motion-selective area MT mirror perception, but strong suppression also occurs in earlier visual areas, and (3) suppression is not primarily driven by GABA-mediated inhibition. Thus, while commonly used spatial suppression paradigms may provide insight into neural response magnitudes in visual areas, they should not be used to infer neural inhibition.
Bibliographical noteFunding Information:
We thank Geoffrey M. Boynton for providing the MATLAB functions for the model, and for comments on the manuscript. We also thank Brenna Boyd, Judy Han, Heena Panjwani, Micah Pepper, Meaghan Thompson, Anne Wolken, the UW Diagnostic Imaging Center, and the UW Investigational Drug Service for their help with subject recruitment and/or data collection. Finally, we thank the reviewers for their helpful comments. This work was supported by funding from the National Institute of Health (F32 EY025121 to MPS, R01 MH106520 to SOM, T32 EY007031, P41 EB015909 and R01 EB016089).
National Eye Institute F32 EY025121 Michael-Paul Schallmo Scott O. Murray National Institute of Mental HealthR01 MH106520 Raphael A Bernier Scott O. Murray National Institute of Biomedical Imaging and Bioengineering P41 EB015909 Richard AE Edden National Eye Institute T32 EY007031 Michael-Paul Schallmo Scott O. Murray National Institute of Biomedical Imaging and Bioengineer- ing R01 EB016089 Richard AE Edden