The prefrontal cortex exerts top-down influences on several aspects of higher-order cognition by functioning as a filtering mechanism that biases bottom-up sensory information toward a response that is optimal in context. However, research also indicates that not all aspects of complex cognition benefit from prefrontal regulation. Here we review and synthesize this research with an emphasis on the domains of learning and creative cognition, and outline how the appropriate level of cognitive control in a given situation can vary depending on the organism's goals and the characteristics of the given task. We offer a Matched Filter Hypothesis for cognitive control, which proposes that the optimal level of cognitive control is task-dependent, with high levels of cognitive control best suited to tasks that are explicit, rule-based, verbal or abstract, and can be accomplished given the capacity limits of working memory and with low levels of cognitive control best suited to tasks that are implicit, reward-based, non-verbal or intuitive, and which can be accomplished irrespective of working memory limitations. Our approach promotes a view of cognitive control as a tool adapted to a subset of common challenges, rather than an all-purpose optimization system suited to every problem the organism might encounter.

Transcranial direct current stimulation (tDCS) is a noninvasive brain stimulation technique used both experimentally and therapeutically to modulate regional brain function. However, few studies have directly measured the aftereffects of tDCS on brain activity or examined changes in task-related brain activity consequent to prefrontal tDCS. To investigate the neural effects of tDCS, we collected fMRI data from 22 human subjects, both at rest and while performing the Balloon Analog Risk Task (BART), before and after true or sham transcranial direct current stimulation. TDCS decreased resting blood perfusion in orbitofrontal cortex and the right caudate and increased task-related activity in the right dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) in response to losses but not wins or increasing risk. Network analysis showed that whole-brain connectivity of the right ACC correlated positively with the number of pumps subjects were willing to make on the BART, and that tDCS reduced connectivity between the right ACC and the rest of the brain. Whole-brain connectivity of the right DLPFC also correlated negatively with pumps on the BART, as prior literature would suggest. Our results suggest that tDCS can alter activation and connectivity in regions distal to the electrodes.

We report a combined behavioral and functional magnetic resonance imaging (fMRI) study of conceptual similarity among members of a natural category (mammals). The study examined the relationship between computed pairwise similarity of neural responses to viewed mammals (e.g. bear, camel, dolphin) and subjective pairwise similarity ratings of the same set of mammals, obtained from subjects after the scanning session. In each functional region of interest (fROI), measures of neural similarity were compared to behavioral ratings. fROIs were identified as clusters of voxels that discriminated intact versus scrambled images of mammals (no information about similarity was used to define fROIs). Neural similarity was well correlated with behavioral ratings in fROIs covering the lateral occipital complex in both hemispheres (with overlap of the fusiform and inferior temporal gyri on the right side). The latter fROIs showed greater hemodynamic response to intact versus scrambled images of mammals whereas the fROIs that failed to predict similarity showed the reverse pattern. The findings provide novel evidence that information about the fine structure of natural categories is coarsely coded in regions of the ventral visual pathway. Implications for the theory of inductive inference are discussed. Keywords Concepts; Reasoning; fMRIInterest in the neural representation of concepts has grown out of the discovery of categoryspecific memory impairments (Warrington & McCarthy, 1987;Warrington & Shallice, 1984) along with the more global degradation of conceptual knowledge known as semantic dementia (Snowden, Goulding, & Neary, 1989;Warrington, 1975). Much of the ensuing research has focused on the extent to which variation across cortical areas is better characterized in category-specific or modality-specific terms. For example, Martin, Wiggs, Ungerleider, & Haxby (1996) discovered that naming both animals and tools activates ventral temporal cortex and Broca's area, while naming only animals activated the left occipital lobe, and naming only tools activated left premotor and middle temporal cortices. (For discussion, see Caramazza &Mahon, 2003, andMartin, 2007.) © 2008 Elsevier Ltd. All rights reserved. * Corresponding author. E-mail address: mattheww@princeton.edu (M. Weber). NIH Public Access Author ManuscriptNeuropsychologia. Author manuscript; available in PMC 2011 January 24.Published in final edited form as: Neuropsychologia. 2009 February ; 47(3): 859-868. doi:10.1016/j.neuropsychologia.2008.029. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptIn a recent review, Tyler et al. (2003) concluded that "the most striking finding in the neuroimaging studies of category and domain specificity is that most categories activate the same neural regions with only weak and inconsistent category-specific effects." The lack of category-specificity suggests shared substrata for diverse concepts, with the identity of a given category coded by the pattern of activation across an entire region. Most curre...

Recent studies of visual statistical learning (VSL) indicate that the visual system can automatically extract temporal and spatial relationships between objects. We report several attempts to replicate and extend earlier work (Turk-Browne et al., 2005) in which observers performed a cover task on one of two interleaved stimulus sets, resulting in learning of temporal relationships that occur in the attended stream, but not those present in the unattended stream. Across four experiments, we exposed observers to a similar or identical familiarization protocol, directing attention to one of two interleaved stimulus sets; afterward, we assessed VSL efficacy for both sets using either implicit response-time measures or explicit familiarity judgments. In line with prior work, we observe learning for the attended stimulus set. However, unlike previous reports, we also observe learning for the unattended stimulus set. When instructed to selectively attend to only one of the stimulus sets and ignore the other set, observers could extract temporal regularities for both sets. Our efforts to experimentally decrease this effect by changing the cover task (Experiment 1) or the complexity of the statistical regularities (Experiment 3) were unsuccessful. A fourth experiment using a different assessment of learning likewise failed to show an attentional effect. Simulations drawing random samples our first three experiments (n=64) confirm that the distribution of attentional effects in our sample closely approximates the null. We offer several potential explanations for our failure to replicate earlier findings, and discuss how our results suggest limiting conditions on the relevance of attention to VSL.

Conceptual combination is an essential cognitive process, yet little is known about its neural correlates. In the present study, a categorization task was used to evoke patterns of neural activation for complex concepts (e.g., young man) as well as their constituents (e.g., young, man). A functional region of interest (fROI) within left anterolateral temporal lobe was identified as a possible site of conceptual combination. In this region, the superimposition of activity for constituent concepts reliably predicted the activation pattern for the complex concept built from those constituents.