Disruption of attention to novel events after frontal lobe injury in humans

Objective-To investigate whether frontal lobe damage in humans disrupts the natural tendency to preferentially attend to novel visual events in the en vironment. Methods-Nine patients with chronic infarctions in the dorsolateral prefront al cortex (DLPFC) and 23 matched normal controls participated in a study in which subjects viewed repetitive background stimuli, infrequent target sti muli, and novel visual stimuli (for example, fragmented or "impossible" obj ects). Subjects controlled viewing duration by a button press that led to t he onset of the next stimulus. They also responded to targets by pressing a foot pedal. The amount of time spent looking at the different kinds of sti muli, and the target detection accuracy and speed served as dependent varia bles. Results-Overall, normal controls spent significantly more time than frontal lobe patients looking at novel stimuli. Analysis of responses across block s showed that initially frontal lobe patients behaved like normal controls by directing more attention to novel than background stimuli. However, they quickly began to distribute their viewing time evenly between novel and ba ckground stimuli, a pattern that was strikingly different from normal contr ols. By contrast, there were no differences between frontal lobe patients a nd normal controls for viewing duration devoted to background and target st imuli, target detection accuracy, or reaction time to targets. Frontal lobe patients did not differ from normal controls in terms of age, education, e stimated IQ, or mood, but were more apathetic as measured by self report an d informants' judgments. Attenuated responses to novel stimuli significantl y correlated with degree of apathy. Conclusions-This study demonstrates that DLPFC injury selectively impairs t he natural tendency to seek stimulation from novel and unusual stimuli. The se data provide the first quantitative behavioural demonstration that the h uman frontal lobes play a critical part in directing and sustaining attenti on to novel events. The impairment of novelty seeking behaviour may contrib ute to the characteristic apathy found in patients with frontal lobe injury .