" The doctors found one electrode contact that greatly relieved the woman's symptoms. But the unexpected happened when the electric current passed through one of the four contact sites on the patient's left side, precisely two millimeters below the contact that improved her condition. The patient stopped her ongoing conversation quite abruptly, cast her eyes down and to her right side, then leaned slightly to the right and her emotional expression became one of sadness. After a few seconds she suddenly began to cry. Tears flowed and her entire demeanor was one of profound misery. Soon she was sobbing. As this display continued she began talking about how deeply sad she felt, how she had no energies left to go on living in this manner, how hopeless and exhausted she was. [ . . . ]

The physician in charge of the treatment realized that this unusual event was due to the current and aborted the procedure. About ninety seconds after the current was interrupted the patient's behavior returned to normal. [ . . . ]

Why would this patient's brain evoke the kind of thoughts that normally cause sadness considering that the emotion and feeling were unmotivated by the appropriate stimuli? The answer has to do with the dependence of feeling on emotion and the intriguing ways of one's memory. When the emotion sadness is deployed, feelings of sadness instantly follow. In short order, the brain also brings forth the kind of thoughts that normally cause the emotion sadness and feelings of sadness. This is because associative learning has linked emotions with thoughts in a rich two-way network. Certain thoughts evoke certain emotions and vice-versa. "

― António R. Damásio , Looking for Spinoza: Joy, Sorrow, and the Feeling Brain