No abstract

The physiological basis for the striking decrease of attention to novel events following frontal lobe injury is poorly understood. In this study, event-related potentials (ERPs) were recorded from patients with frontal lobe damage and matched subjects, who controlled the duration of viewing of background, novel and target stimuli. Frontal lobe patients did not differ from normal controls in terms of age, education, estimated IQ or mood. However, they were judged to be more apathetic as measured by self-report and informants' ratings. Patients with frontal lobe damage exhibited markedly reduced amplitude of the novelty P3 response and the duration of viewing of novel stimuli. In contrast, injury to the frontal lobes had a limited impact on P3 amplitude and behavioural responses (viewing duration and reaction time) to target stimuli. A strong correlation was found between measures of apathy and both attenuated P3 amplitude and viewing duration in response to novel but not target stimuli. Differences in amplitude of the novelty P3 response explained a large portion of the variance associated with duration of viewing of novel stimuli. After controlling for the influence of P3 amplitude, there was no association between frontal lobe injury and reduced viewing of novel stimuli. The results of this study suggest that frontal lobe damage leads to diminished visual attention to novel events through its disruption of neural processes underlying the novelty P3 response. These processes appear to regulate the allocation of attentional resources and early exploratory behaviours, and are not limited to immediate orienting responses. Damage to the frontal lobes may prevent the generation of a signal which indicates that a novel event in the environment requires additional attention due to its potential behavioural significance. The disruption of these processes is likely to contribute to the apathy observed in patients after injury to the frontal lobes.

No abstract

Objective-To investigate whether frontal lobe damage in humans disrupts the natural tendency to preferentially attend to novel visual events in the environment. Methods-Nine patients with chronic infarctions in the dorsolateral prefrontal cortex (DLPFC) and 23 matched normal controls participated in a study in which subjects viewed repetitive background stimuli, infrequent target stimuli, and novel visual stimuli (for example, fragmented or "impossible" objects). Subjects controlled viewing duration by a button press that led to the onset of the next stimulus. They also responded to targets by pressing a foot pedal. The amount of time spent looking at the diVerent kinds of stimuli, and the target detection accuracy and speed served as dependent variables. Results-Overall, normal controls spent significantly more time than frontal lobe patients looking at novel stimuli. Analysis of responses across blocks 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 background stimuli, a pattern that was strikingly diVerent from normal controls. By contrast, there were no diVerences between frontal lobe patients and normal controls for viewing duration devoted to background and target stimuli, target detection accuracy, or reaction time to targets. Frontal lobe patients did not diVer from normal controls in terms of age, education, estimated IQ, or mood, but were more apathetic as measured by self report and informants' judgments. Attenuated responses to novel stimuli significantly correlated with degree of apathy. Conclusions-This study demonstrates that DLPFC injury selectively impairs the natural tendency to seek stimulation from novel and unusual stimuli. These data provide the first quantitative behavioural demonstration that the human frontal lobes play a critical part in directing and sustaining attention to novel events. The impairment of novelty seeking behaviour may contribute to the characteristic apathy found in patients with frontal lobe injury. (J Neurol Neurosurg Psychiatry 2000;68:18-24)