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Attention dysfunction is a common but often undiagnosed cognitive impairment in Parkinson's disease that significantly reduces quality of life. We sought to increase understanding of the mechanisms underlying attention dysfunction using functional neuroimaging. Functional MRI was acquired at two repeated sessions in the resting state and during the Attention Network Test, for 25 non-demented subjects with Parkinson's disease and 21 healthy controls. Behavioral and MRI contrasts were calculated for alerting, orienting, and executive control components of attention. Brain regions showing group differences in attention processing were used as seeds in a functional connectivity analysis of a separate resting state run. Parkinson's disease subjects showed more activation during increased executive challenge in four regions of the dorsal attention and frontoparietal networks, namely right frontal eye field, left and right intraparietal sulcus, and precuneus. In three regions we saw reduced resting state connectivity to the default mode network. Further, whereas higher task activation in the right intraparietal sulcus correlated with reduced resting state connectivity between right intraparietal sulcus and the precuneus in healthy controls, this relationship was absent in Parkinson's disease subjects. Our results suggest that a weakened interaction between the default mode and task positive networks might alter the way in which the executive response is processed in PD.

Synchronized phase estimates between oscillating neuronal signals at the macroscale level reflect coordinated activities between neuronal assemblies. Recent electrophysiological evidence suggests the presence of significant spontaneous phase synchrony within the resting state. The purpose of this study was to investigate phase synchrony, including directional interactions, in resting state subdural electrocorticographic recordings to better characterize patterns of regional phase interactions across the lateral cortical surface during the resting state. We estimated spontaneous phase locking value (PLV) as a measure of functional connectivity, and phase slope index (PSI) as a measure of pseudo-causal phase interactions, across a broad range of canonical frequency bands and the modulation of the amplitude envelope of high gamma (amHG), a band that is believed to best reflect the physiological processes giving rise to the functional magnetic resonance imaging BOLD signal. Long-distance interactions had higher PLVs in slower frequencies (≤theta) than in higher ones (≥beta) with amHG behaving more like slow frequencies, and a general trend of increasing frequency band of significant PLVs when moving across the lateral surface along an anterior-posterior axis. Moreover, there was a strong trend of frontal-to-parietal directional phase synchronization, measured by PSI across multiple frequencies. These findings, which are likely indicative of coordinated and structured spontaneous cortical interactions, are important in the study of time scales and directional nature of resting state functional connectivity, and may ultimately contribute to a better understanding of how spontaneous synchrony is linked to variation in regional architecture across the lateral cortical surface.

Cortical dysfunction in Parkinson's disease (PD) may be caused by disruption to ascending systems or by intrinsic cortical neuropathology. We introduce and conduct a joint analysis of metabolism and atrophy capable of identifying whether metabolic disruption occurs in mild PD without cortical atrophy, to determine the extent and spatial pattern of cortical involvement in mild PD. The design was observational, studying 23 cognitively normal participants with mild PD (mean Hoehn & Yahr stage 2) and 21 healthy controls. Cortical thickness (obtained from analysis of structural magnetic resonance imaging [MRI] with FreeSurfer) and cerebral perfusion measures (obtained from arterial spin labeling [ASL]) analyzed independently and then together in a joint multiple factorial analysis to identify spatial patterns of perfusion and cortical thickness. We identify a pattern of changes in perfusion and cortical thickness characterized by symmetric parietal cortical thinning and reduced precuneus perfusion, with relative preservation of thickness and perfusion in the anterior cingulate cortex (ACC), right prefrontal gyrus, and medial frontal gyrus. The expression of this pattern is correlated with motor system symptoms and speed of processing. A spatial pattern of joint parietal cortical thinning and disproportionate reduction in perfusion occurs in our nondemented PD sample. We found no PD-related components of reduced perfusion without cortical thinning. This suggests that PD affects the cortex itself, even when symptoms are relatively mild., (© 2015 International Parkinson and Movement Disorder Society.)

Connectivity information derived from diffusion MRI can be used to parcellate the cerebral cortex into anatomically and functionally meaningful subdivisions. Acquisition and processing parameters can significantly affect parcellation results, and there is no consensus on best practice protocols. We propose a novel approach for evaluating parcellation based on measuring the degree to which parcellation conforms to known principles of brain organization, specifically cortical field homogeneity and interhemispheric homology. The proposed metrics are well behaved on morphologically generated whole-brain parcels, where they correctly identify contralateral homologies and give higher scores to anatomically versus arbitrarily generated parcellations. The measures show that individual cortical fields have characteristic connectivity profiles that are compact and separable, and that the topological arrangement of such fields is strongly conserved between hemispheres and individuals. The proposed metrics can be used to evaluate the quality of parcellations at the subject and group levels and to improve acquisition and data processing for connectivity-based cortical parcellation.

Biological differences between signed and spoken languages may be most evident in the expression of spatial information. PET was used to investigate the neural substrates supporting the production of spatial language in American Sign Language as expressed by classifier constructions, in which handshape indicates object type and the location/motion of the hand iconically depicts the location/motion of a referent object. Deaf native signers performed a picture description task in which they overtly named objects or produced classifier constructions that varied in location, motion, or object type. In contrast to the expression of location and motion, the production of both lexical signs and object type classifier morphemes engaged left inferior frontal cortex and left inferior temporal cortex, supporting the hypothesis that unlike the location and motion components of a classifier construction, classifier handshapes are categorical morphemes that are retrieved via left hemisphere language regions. In addition, lexical signs engaged the anterior temporal lobes to a greater extent than classifier constructions, which we suggest reflects increased semantic processing required to name individual objects compared with simply indicating the type of object. Both location and motion classifier constructions engaged bilateral superior parietal cortex, with some evidence that the expression of static locations differentially engaged the left intraparietal sulcus. We argue that bilateral parietal activation reflects the biological underpinnings of sign language. To express spatial information, signers must transform visual-spatial representations into a body-centered reference frame and reach toward target locations within signing space.

The production of sign language involves two large articulators (the hands) moving through space and contacting the body. In contrast, speech production requires small movements of the tongue and vocal tract with no observable spatial contrasts. Nonetheless, both language types exhibit a sublexical layer of structure with similar properties (e.g., segments, syllables, feature hierarchies). To investigate which neural areas are involved in modality-independent language production and which are tied specifically to the input-output mechanisms of signed and spoken language, we reanalyzed PET data collected from 29 deaf signers and 64 hearing speakers who participated in a series of separate studies. Participants were asked to overtly name concrete objects from distinct semantic categories in either American Sign Language (ASL) or in English. The baseline task required participants to judge the orientation of unknown faces (overtly responding 'yes'/'no' for upright/inverted). A random effects analysis revealed that left mesial temporal cortex and the left inferior frontal gyrus were equally involved in both speech and sign production, suggesting a modality-independent role for these regions in lexical access. Within the left parietal lobe, two regions were more active for sign than for speech: the supramarginal gyrus (peak coordinates: -60, -35, +27) and the superior parietal lobule (peak coordinates: -26, -51, +54). Activation in these regions may be linked to modality-specific output parameters of sign language. Specifically, activation within left SMG may reflect aspects of phonological processing in ASL (e.g., selection of hand configuration and place of articulation features), whereas activation within SPL may reflect proprioceptive monitoring of motoric output.

Cognitive models of word production correlate the word frequency effect (i.e., the fact that words which appear with less frequency take longer to produce) with an increased processing cost to activate the whole-word (lexical) phonological representation. We performed functional magnetic resonance imaging (fMRI) while subjects produced overt naming responses to photographs of animals and manipulable objects that had high name agreement but were of varying frequency, with the purpose of identifying neural structures participating specifically in activating whole-word phonological representations, as opposed to activating lexical semantic representations or articulatory-motor routines. Blood oxygen level-dependent responses were analyzed using a parametric approach based on the frequency with which each word produced appears in the language. Parallel analyses were performed for concept familiarity and word length, which provided indices of semantic and articulatory loads. These analyses permitted us to identify regions related to word frequency alone, and therefore, likely to be related specifically to activation of phonological word forms. We hypothesized that the increased processing cost of producing lower-frequency words would correlate with activation of the left posterior inferotemporal (IT) cortex, the left posterior superior temporal gyrus (pSTG), and the left inferior frontal gyrus (IFG). Scan-time response latencies demonstrated the expected word frequency effect. Analysis of the fMRI data revealed that activity in the pSTG was modulated by frequency but not word length or concept familiarity. In contrast, parts of IT and IFG demonstrated conjoint frequency and familiarity effects, and parts of both primary motor regions demonstrated conjoint effects of frequency and word length. The results are consistent with a model of word production in which lexical-semantic and lexical-phonological information are accessed by overlapping neural systems within posterior and anterior language-related cortices, with pSTG specifically involved in accessing lexical phonology.

The neural correlates of naming concrete entities such as tools (with nouns) and naming actions (with verbs) are partially distinct: the former are linked to the left inferotemporal (IT) region, whereas the latter are linked to the left frontal opercular (FO) and left posterior middle temporal (MT) regions. This raises an intriguing question: How would such neural patterns be influenced by noun-verb homonymy, specifically, naming tasks in which the target words denote objects or actions (e.g., "comb")? To explore this, we conducted a PET study in which 10 normal participants named visually presented tools or actions. The factor of homonymy yielded interesting effects: For tools, non-homonymous nouns (e.g., "camera") activated left IT, whereas homonymous nouns (e.g., "comb") activated both left IT and left FO. For actions, non-homonymous (e.g., "juggle") and homonymous (e.g., "comb") verbs activated left FO, MT, and IT, but there was evidence that the FO and MT activations were less widespread for the homonymous verbs. We also found that retrieval of the same exact words (e.g., "comb" and "comb") produced differential activation in left MT-there was greater MT activation when the words were being used to name actions, than when they were being used to name tools. Our results suggest that noun-verb homonymy has an important influence on the patterns of neural activation associated with words denoting objects and actions, and that even when the phonological forms are identical, the patterns of neural activation are different according to the demands of the task.

Functional magnetic resonance imaging (fMRI) is used as an alternative to positron emission tomogaphy (PET). It is inexpensive, uses no radionuclides and does not require doctors compared to PET. fMRI generates images at 50 msec which is also the rate of neural processes. Randy Buckner and associates have made fMRI single measurements without resorting to repeated cognition tasks. It is now possible to sort trials post facto by subject performance which is difficult to do in blocked tasks. This will allow for more flexibility in experimental design.

In a series of [[sup 15]O]PET experiments aimed at investigating the neural basis of emotion and feeling, 41 normal subjects recalled and re-experienced personal life episodes marked by sadness, happiness, anger or fear. We tested the hypothesis that the process of feeling emotions requires the participation of brain regions, such as the somatosensory cortices and the upper brainstem nuclei, that are involved in the mapping and/or regulation of internal organism states. Such areas were indeed engaged, underscoring the close relationship between emotion and homeostasis. The findings also lend support to the idea that the subjective process of feeling emotions is partly grounded in dynamic neural maps, which represent several aspects of the organism's continuously changing internal state. [ABSTRACT FROM AUTHOR]