Effects of Acute Stress or Centrally Injected Interleukin-1beta on Neuropeptide Expression in the Immune System

Acute stress stimulates the expression and release of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) from the hypothalamus, and the pro-opiomelanocortin products beta-endorphin and ACTH from the anterior pituitary. These neuropeptides are also expressed in immune tissues, and it has been proposed that they may modulate immune responses to stress through paracrine mechanisms. We subjected rats to restraint stress or central injection of interleukin (IL)-1beta to determine whether these acute stimuli can alter the expression of neuropeptides in the spleen and thymus. Restraint stress significantly increased the contents of all these neuropeptides in thymic, but not splenic, extracts. A single icv injection of IL-1beta increased contents of CRH, AVP, ACTH and beta-endorphin in the spleens of both sham-operated and adrenalectomised (ADX) rats. IL-1beta increased thymic contents of CRH and ACTH in sham-operated rats but these increases were not observed in ADX rats. These results suggest that the effects of IL-1beta on neuropeptide expression in the spleen are independent of glucocorticoids, whereas IL-1beta stimulation of neuropeptide expression in the thymus is dependent on circulating glucocorticoids. There were significant correlations between increases in CRH, ACTH and beta-endorphin in the spleen, and between CRH and ACTH in the thymus, consistent with the suggestion that IL-1beta-induced increases in ACTH and beta-endorphin may be mediated through CRH. These results provide evidence that stressors can directly influence neuropeptide expression in immune tissues. Thus stress may influence immune functions through paracrine mechanisms involving locally synthesised neuropeptides as well as through activation of the hypothalamo-pituitary-adrenal axis.     

Dorsal stream activation during retrieval of object size and shape

We investigated dorsal visual stream involvement in the retrieval of a variety of visual attributes of common objects, using functional magnetic resonance imaging. Seven subjects made binary decisions about the shape, color, and size of named objects during scanning. Bilateral parietal activity was significantly greater during retrieval of shape and size information than during retrieval of color information. Consistent with a domain-specific distributed model of semantic organization, the finding that dorsal stream activity is associated with size and shape retrieval, as compared with color retrieval, may indicate that both size and shape information are learned partly through dorsally mediated processes, such as visually guided grasping. These results demonstrate that both visual-processing streams (i.e., the ventral “what” pathway and the dorsal “where” pathway) are involved in the storage and/or retrieval of knowledge of object appearance but that, just as in vision, these two pathways may play different roles in conceptual processing.     

Colorless green ideas (can) prime furiously

That similar words can prime one another is not news. However, this phenomenon can be exploited to make inferences about the organization of conceptual representations. What types of similarity matter? Although there is evidence that similarity of function, shape, and even manner of manipulation is reflected in semantic memory, evidence for organization on the basis of color similarity is sparse. This lack of evidence is surprising: Intuition suggests that color is a prominent feature of many object concepts. The research reported here clarifies this puzzle and illustrates the dynamic nature of conceptual representations. Our research demonstrates color-based priming (e.g., "emerald" primes "cucumber") in participants who completed a Stroop color-naming task before a priming task. Notably, the size of the Stroop effect predicted the size of the priming effect. When the order of tasks was reversed, priming effects were eliminated. By demonstrating that both extrinsic and intrinsic factors can influence conceptual activation, our findings have implications for theories of semantic memory.     

Resolving conflict: A response to Martin and Cheng (2006)

Martin and Cheng (2006) report the results of an experiment aimed at disentangling the effects of association strength from those of competition on performance on a verb generation task. Their experiment is situated at the center of a putative debate regarding the function of the left inferior frontal gyrus in language processing (see, e.g., Wagner, Paré-Blagoev, Clark, & Poldrack, 2001). Following in this tradition, Martin and Cheng purport to contrast two processes—selection between competing representations and controlled retrieval of weak associates—that we argue can be reduced to the same mechanism. We contend that the distinction between competition and association strength is a false dichotomy, and we attempt to recast this discussion within a Bayesian framework in an attempt to guide research in this area in a more fruitful direction.     

Reproducibility of functional network metrics and network structure: A comparison of task-related BOLD, resting ASL with BOLD contrast, and resting cerebral blood flow

Network analysis is an emerging approach to functional connectivity in which the brain is construed as a graph and its connectivity and information processing estimated by mathematical characterizations of graphs. There has been little to no work examining the reproducibility of network metrics derived from different types of functional magnetic resonance imaging (fMRI) data (e.g., resting vs. task related, or pulse sequences other than standard blood oxygen level dependent [BOLD] data) or of measures of network structure at levels other than summary statistics. Here, we take up these questions, comparing the reproducibility of graphs derived from resting arterial spin-labeling perfusion fMRI with those derived from BOLD scans collected while the participant was performing a task. We also examine the reproducibility of the anatomical connectivity implied by the graph by investigating test–retest consistency of the graphs’ edges. We compare two measures of graph-edge consistency both within versus between subjects and across data types. We find a dissociation in the reproducibility of network metrics, with metrics from resting data most reproducible at lower frequencies and metrics from task-related data most reproducible at higher frequencies; that same dissociation is not recapitulated, however, in network structure, for which the task-related data are most consistent at all frequencies. Implications for the practice of network analysis are discussed.     

Developmental "Roots" in Mature Biological Knowledge

ABSTRACT— Young children tend to claim that moving artifacts and nonliving natural kinds are alive, but neglect to ascribe life to plants. This research tested whether adults exhibit similar confusions when verifying life status in a speeded classification task. Experiment 1 showed that undergraduates encounter greater difficulty (reduced accuracy and increased response times) in determining life status for plants, relative to animals, and for natural and moving nonliving things, relative to artifacts and nonmoving things. Experiment 2 replicated these effects in university biology professors. The professors showed a significantly reduced effect size for living things, as compared with the students, but still showed greater difficulty for plants than animals, even as no differences from the students were apparent in their responses to nonliving things. These results suggest that mature biological knowledge relies on a developmental foundation that is not radically overwritten or erased with the profound conceptual changes that accompany mastery of the domain.     

Effect of name agreement on prefrontal activity during overt and covert picture naming

In recent neuroimaging studies, various tasks have been used to examine prefrontal cortex involvement in semantic retrieval and selection. One such task, picture naming, has yielded inconsistent results across studies. One potential explanation for this inconsistency is that the magnitude of prefrontal activity during picture naming depends on the extent to which a given picture evokes a single reliable meaning. To test this hypothesis, fMRI activity in the prefrontal cortex was measured while subjects named pictures with either high or low name agreement. In Experiment 1, subjects named black-andwhite line drawings, either covertly or overtly. Across both modalities, we found more left inferior frontal gyrus (LIFG) activity when the subjects named low-agreement pictures than when they named high-agreement pictures. No significant difference in head movement was detected between the two modalities. In Experiment 2, we replicated the effect of name agreement on LIFG activity during picture naming, using black-and-white photographs. These results provide further support for the idea that the LIFG mediates selection among competing alternatives and suggest a means for understanding the naming deficits observed in nonfluent aphasia.     

Convergent behavioral and neuropsychological evidence for a distinction between identification and production forms of repetition priming

Four experiments examined a distinction between kinds of repetition priming which involve either the identification of the form or meaning of a stimulus or the production of a response on the basis of a cue. Patients with Alzheimer's disease had intact priming on picture-naming and category-exemplar identification tasks and impaired priming on word-stem completion and category-exemplar production tasks. Division of study-phase attention in healthy participants reduced priming on word-stem completion and category-exemplar production tasks but not on picture-naming and category-exemplar identification tasks. The parallel dissociations in normal and abnormal memory cannot be explained by implicit-explicit or perceptual-conceptual distinctions but are explained by an identification-production distinction. There may be separable cognitive and neural bases for implicit modulation of identification and production forms of knowledge.