Humans are a social species that engage in complex interactions during goal-oriented cooperation.¹ Social cognition is the basis for such interactions and includes three main components: simulation, empathy, and mentalization. The standard simulation notion refers to a functional process in which an observer tries to voluntarily reproduce, even with the help of imagination, the same mental states of another individual.² First, social cognition has been attributed by Gallese³ to an embodied simulation enabling an immediate understanding and associated with mirror neuron systems, i.e., neuronal systems that are activated when an intentional action is performed (such as motor action) and when the observing the same action. Studies have shown activation of the motor cortex in 6-month-old children when observing actions.^4,5 The second component is empathy, which is defined as the ability to share feelings and emotions.⁶ It is automatic, different for everyone and it is stronger depending on the type of relationship one has with the observed person.^7,8 Third, mentalization is an essential part of social cognition and the ability to read the state of mind, such as desires, beliefs, and intentions in others.^{9 – 11}

Functional imaging has struggled for two decades to establish a quantitative link between the neuronal activity and the change in signal obtained. This review proposes a division of neuronal activity into a component relating to the electrical discharge activity and a component relating to the size of the activated neuronal population. These two components are argued to have opposing influences on the BOLD signal. The influence of these two components on the BOLD signal, are summarised in the standard model.