Here we review 37 modern neuroimaging studies in an attempt to address this question posed by Halstead (1947) as he and other icons of the last century endeavored to understand how brain and behavior are linked through the expression of intelligence and reason. Reviewing studies from functional (i.e., functional magnetic resonance imaging, positron emission tomography) and structural (i.e., magnetic resonance spectroscopy, diffusion tensor imaging, voxel-based morphometry) neuroimaging paradigms, we report a striking consensus suggesting that variations in a distributed network predict (...) individual differences found on intelligence and reasoning tasks. We describe this network as the Parieto-Frontal Integration Theory (P-FIT). The P-FIT model includes, by Brodmann areas (BAs): the dorsolateral prefrontal cortex (BAs 6, 9, 10, 45, 46, 47), the inferior (BAs 39, 40) and superior (BA 7) parietal lobule, the anterior cingulate (BA 32), and regions within the temporal (BAs 21, 37) and occipital (BAs 18, 19) lobes. White matter regions (i.e., arcuate fasciculus) are also implicated. The P-FIT is examined in light of findings from human lesion studies, including missile wounds, frontal lobotomy/leukotomy, temporal lobectomy, and lesions resulting in damage to the language network (e.g., aphasia), as well as findings from imaging research identifying brain regions under significant genetic control. Overall, we conclude that modern neuroimaging techniques are beginning to articulate a biology of intelligence. We propose that the P-FIT provides a parsimonious account for many of the empirical observations, to date, which relate individual differences in intelligence test scores to variations in brain structure and function. Moreover, the model provides a framework for testing new hypotheses in future experimental designs. (shrink)

Conscious experience is one of the most difficult and thorny problems in psychological science. Its study has been neglected for many years, either because it was thought to be too difficult, or because the relevant evidence was thought to be poor. Bernard Baars suggests a way to specify empirical constraints on a theory of consciousness by contrasting well-established conscious phenomena - such as stimulus representations known to be attended, perceptual, and informative - with closely comparable unconscious ones - such as (...) stimulus representations known to be preperceptual, unattended, or habituated. Adducing data to show that consciousness is associated with a kind of global workplace in the nervous system, and that several brain structures are known to behave in accordance with his theory, Baars helps to clarify many difficult problems. (shrink)

1 INSERM-CEA Unit 562, Cognitive Neuroimaging, Service Hospitalier Fre´de´ric Joliot, Orsay, France, 2 CNRS URA2182 Re´cepteurs and Cognition, Institut Pasteur, Paris, France.

Task unrelated thought refers to thought directed away from the current situation; for example, a day dream. Encapsulated models of cognition propose that qualitative changes in consciousness, i.e., the production of TUT, can be explained in terms of changes in the quantity of resources deployed for task completion. In contrast, distributed models of cognition emphasize the importance of holistic processes in the generation and maintenance of task focus and are consistent with the effects of higher order variables such as schemata. (...) Three experiments were conducted on healthy participants using a categorical stimulus organization to contrast distributed and encapsulated views of cognition. Experiments 1 and 2 showed that despite the increased difficulty of the alphabetical verbal fluency task fewer TUTs were produced during category fluency condition. Experiment 3 replicated the categorical suppression of TUT while encoding and recalling information in a memory task. The results of these three experiments support the predictions derived from models of cognition emphasizing the importance of stimulus organization in the generation and maintenance of task focus and have potential importance for the scientific evaluation of cognition. (shrink)

The capacity to self-generate mental content that is unrelated to the current environment is a fundamental characteristic of the mind, and the current experiment explored how this experience is related to the decisions that people make in daily life. We examined how task-unrelated thought varies with the length of time participants are willing to wait for an economic reward, as measured using an inter-temporal discounting task. When participants performed a task requiring minimal attention, the greater the amount of time spent (...) engaged in TUT the longer the individual was prepared to wait for an economic reward. These data indicate that self-generated thought engages processes associated with the successful management of long-term goals. Although immersion in the here and now is undeniably advantageous, under appropriate conditions the capacity to let go of the present and consider more pertinent personal goals may have its own rewards. (shrink)

Given that as much as half of human thought arises in a stimulus independent fashion, it would seem unlikely that such thoughts would play no functional role in our lives. However, evidence linking the mind-wandering state to performance decrement has led to the notion that mind-wandering primarily represents a form of cognitive failure. Based on previous work showing a prospective bias to mind-wandering, the current study explores the hypothesis that one potential function of spontaneous thought is to plan and anticipate (...) personally relevant future goals, a process referred to as autobiographical planning. The results confirm that the content of mind-wandering is predominantly future-focused, demonstrate that individuals with high working memory capacity are more likely to engage in prospective mind-wandering, and show that prospective mind-wandering frequently involves autobiographical planning. Together this evidence suggests that mind-wandering can enable prospective cognitive operations that are likely to be useful to the individual as they navigate through their daily lives. (shrink)

Current accounts suggest that self-referential thought serves a pivotal function in the human ability to simulate the future during mind-wandering. Using experience sampling, this hypothesis was tested in two studies that explored the extent to which self-reflection impacts both retrospection and prospection during mind-wandering. Study 1 demonstrated that a brief period of self-reflection yielded a prospective bias during mind-wandering such that participants’ engaged more frequently in spontaneous future than past thought. In Study 2, individual differences in the strength of self-referential (...) thought — as indexed by the memorial advantage for self rather than other-encoded items — was shown to vary with future thinking during mind-wandering. Together these results confirm that self-reflection is a core component of future thinking during mind-wandering and provide novel evidence that a key function of the autobiographical memory system may be to mentally simulate events in the future. (shrink)

Thought-intrusions, automatic inferences, and other unintended thought are beginning to play an important role in the study of psychiatric disease as well as normal thought processes. We examine one method for study of task-unrelated imagery and thought . TUIT likelihood was shown to be reliably measured over a wide range of vigilance tasks, to have high short-term and long-term test-retest reliability, and to be sensitive to information processing demands. Likelihood of TUITs was shown to be different as a function of (...) aging, hyperactivity, time of day, and level of depression. Thus, we now can reliably measure the influence of endogenous and exogenous influences on TUITs. In addition, TUIT measurement was proposed as a minimally interfering and natural second task for determining resource utilization in a primary task. Finally, this method was offered as a reliable approach to quantification of such mental states as obsessions and drug craving and addiction. (shrink)