This study investigates the role of parvalbumin (PV) interneurons and gamma oscillations in cortical circuit performance. Using optogenetic techniques, the authors selectively modulated PV interneurons in mice to test their functional significance. They found that inhibiting PV interneurons suppressed gamma oscillations, while stimulating these interneurons generated gamma-frequency rhythmicity. Gamma-frequency modulation of excitatory input was shown to enhance signal transmission in neocortex by reducing circuit noise and amplifying signals, including inputs to PV interneurons. The study also demonstrated that gamma oscillations increased mutual information between input and output signals, enhancing information processing. These findings highlight the critical role of PV interneurons and gamma oscillations in modulating cortical circuit function and suggest that abnormalities in these mechanisms may contribute to cognitive disorders such as schizophrenia and autism.This study investigates the role of parvalbumin (PV) interneurons and gamma oscillations in cortical circuit performance. Using optogenetic techniques, the authors selectively modulated PV interneurons in mice to test their functional significance. They found that inhibiting PV interneurons suppressed gamma oscillations, while stimulating these interneurons generated gamma-frequency rhythmicity. Gamma-frequency modulation of excitatory input was shown to enhance signal transmission in neocortex by reducing circuit noise and amplifying signals, including inputs to PV interneurons. The study also demonstrated that gamma oscillations increased mutual information between input and output signals, enhancing information processing. These findings highlight the critical role of PV interneurons and gamma oscillations in modulating cortical circuit function and suggest that abnormalities in these mechanisms may contribute to cognitive disorders such as schizophrenia and autism.