Left dorsolateral prefrontal cortex supports context-dependent prioritisation of off-task thought.

When environments lack compelling goals, humans often let their minds wander to thoughts with greater personal relevance; however, we currently do not understand how this context-dependent prioritisation process operates. Dorsolateral prefrontal cortex (DLPFC) maintains goal representations in a context-dependent manner. Here, we show this region is involved in prioritising off-task thought in an analogous way. In a whole brain analysis we established that neural activity in DLPFC is high both when 'on-task' under demanding conditions and 'off-task' in a non-demanding task. Furthermore, individuals who increase off-task thought when external demands decrease, show lower correlation between neural signals linked to external tasks and lateral regions of the DMN within DLPFC, as well as less cortical grey matter in regions sensitive to these external task relevant signals. We conclude humans prioritise daydreaming when environmental demands decrease by aligning cognition with their personal goals using DLPFC.

The inferior, anterior temporal lobes and semantic memory clarified: novel evidence from distortion-corrected fMRI.

The neural basis of semantic memory generates considerable debate. Semantic dementia results from bilateral anterior temporal lobe (ATL) atrophy and gives rise to a highly specific impairment of semantic memory, suggesting that this region is a critical neural substrate for semantic processing. Recent rTMS experiments with neurologically-intact participants also indicate that the ATL are a necessary substrate for semantic memory. Exactly which regions within the ATL are important for semantic memory are difficult to detect from these methods (because the damage in SD covers a large part of the ATL). Functional neuroimaging might provide important clues about which specific areas exhibit activation that correlates with normal semantic performance. Neuroimaging studies, however, have not consistently found anterior temporal lobe activation in semantic tasks. A recent meta-analysis indicates that this inconsistency may be due to a collection of technical limitations associated with previous studies, including a reduced field-of-view and magnetic susceptibility artefacts associated with standard gradient echo fMRI. We conducted an fMRI study of semantic memory using a combination of techniques which improve sensitivity to ATL activations whilst preserving whole-brain coverage. As expected from SD patients and ATL rTMS experiments, this method revealed bilateral temporal activation extending from the inferior temporal lobe along the fusiform gyrus to the anterior temporal regions, bilaterally. We suggest that the inferior, anterior temporal lobe region makes a crucial contribution to semantic cognition and utilising this version of fMRI will enable further research on the semantic role of the ATL.

Semantic processing in the anterior temporal lobes: a meta-analysis of the functional neuroimaging literature.

The role of the anterior temporal lobes (ATLs) in semantic cognition is not clear from the current literature. Semantic dementia patients show a progressive and a specific semantic impairment, following bilateral atrophy of the ATLs. Neuroimaging studies of healthy participants, however, do not consistently show ATL activation during semantic tasks. Consequently, several influential theories of semantic memory do not ascribe a central role to the ATLs. We conducted a meta-analysis of 164 functional neuroimaging studies of semantic processing to investigate factors that might contribute to the inconsistency in previous results. Four factors influenced the likelihood of finding ATL activation: (1) the use of PET versus fMRI, reflecting the fact that fMRI but not PET is sensitive to distortion artifacts caused by large variations in magnetic susceptibility in the area of the ATL; (2) a field of view (FOV) of more than 15 cm, thereby ensuring whole-brain coverage; (3) the use of a high baseline task to prevent subtraction of otherwise uncontrolled semantic activation; (4) the inclusion of the ATL as an ROI. The type of stimuli or task did not influence the likelihood of ATL activation, consistent with the view that this region underpins an amodal semantic system. Spoken words, written words, and picture stimuli produced overlapping ATL peaks. On average, these were more inferior for picture-based tasks. We suggest that the specific pattern of ATL activation may be influenced by stimulus type due to variations across this region in the degree of connectivity with modality-specific areas in posterior temporal cortex.