Hatred or hate is a word that describes intense feelings of dislike. It can be used in a wide variety of contexts, from hatred of inanimate objects (e.g. homework, vegetables) to hatred of other people, or even groups of people. Philosophers have offered many influential definitions of hatred. Rene Descartes viewed hate as an awareness that something is bad, combined with an urge to withdraw from it. Baruch Spinoza defined hate as a type of pain that is due to an external cause. Aristotle viewed hate as a desire for the annihilation of an object that is incurable by time. Finally, David Hume believed that hate is an irreducible feeling that is not definable at all. In psychology, Sigmund Freud defined hate as an ego state that wishes to destroy the source of its unhappiness. In a more contemporary definition, the Penguin Dictionary of Psychology defines hate as a "deep, enduring, intense emotion expressing animosity, anger, and hostility towards a person, group, or object." Because hatred is believed to be long-lasting, many psychologists consider it to be more of an attitude or disposition than a (temporary) emotional state. The neural correlates of hate have been investigated with an fMRI procedure. In this experiment, people had their brains scanned while viewing pictures of people they hated. The results showed increased activity in the medial frontal gyrus, right putamen, bilaterally in the premotor cortex, in the frontal pole, and bilaterally in the medial insula of the human brain. The researchers concluded that there is a distinct pattern of brain activity that occurs when people are experiencing hatred.