This paper introduces the concept of psychophysiological interactions (PPIs) in neuroimaging, which refer to interactions between the influence of one brain area and an experimental parameter (e.g., sensory or task-related). These interactions are distinct from conventional psychological interactions and physiological interactions. PPIs are framed in terms of functional integration, where the contribution of one area to another is modulated by experimental or psychological context. The paper discusses how PPIs can be modeled using regression analyses and statistical parametric mapping (SPM), and illustrates this with examples from functional MRI (fMRI) and positron emission tomography (PET) studies. It highlights the importance of PPIs in understanding how brain regions interact in response to different experimental conditions, such as attention to visual motion and visual priming. The paper also discusses the distinction between effective connectivity (the influence one area has on another) and functional connectivity (correlations between areas). It emphasizes that PPIs allow for a more nuanced understanding of how brain regions interact, particularly in context-sensitive ways. The paper concludes that PPIs provide a valuable framework for interpreting neuroimaging data and understanding the functional organization of the brain.This paper introduces the concept of psychophysiological interactions (PPIs) in neuroimaging, which refer to interactions between the influence of one brain area and an experimental parameter (e.g., sensory or task-related). These interactions are distinct from conventional psychological interactions and physiological interactions. PPIs are framed in terms of functional integration, where the contribution of one area to another is modulated by experimental or psychological context. The paper discusses how PPIs can be modeled using regression analyses and statistical parametric mapping (SPM), and illustrates this with examples from functional MRI (fMRI) and positron emission tomography (PET) studies. It highlights the importance of PPIs in understanding how brain regions interact in response to different experimental conditions, such as attention to visual motion and visual priming. The paper also discusses the distinction between effective connectivity (the influence one area has on another) and functional connectivity (correlations between areas). It emphasizes that PPIs allow for a more nuanced understanding of how brain regions interact, particularly in context-sensitive ways. The paper concludes that PPIs provide a valuable framework for interpreting neuroimaging data and understanding the functional organization of the brain.