Increased neural sensitivity to self-relevant stimuli in major depressive disorder.

The current research examined how individuals with depression process emotional, self-relevant stimuli. Across two studies, individuals with depression and healthy controls read stimuli that varied in self-relevance while EEG data were recorded. We examined the late positive potential (LPP), an ERP component that captures the dynamic allocation of attention to motivationally salient stimuli. In Study 1, participants read single words in a passive-viewing task. Participants viewed negative, positive, or neutral words that were either normative or self-generated. Exploratory analyses indicated that participants with depression exhibited affective modulation of the LPP for self-generated stimuli only (both positive and negative) and not for normative stimuli; healthy controls exhibited similar affective modulation of the LPP for both self-relevant and normative stimuli. In Study 2, using a separate sample and a different task, stimuli were provided within the context of sentence stems referring to the self or other people. Participants with depression were more likely to endorse negative self-referent sentences and reject positive ones compared to healthy controls. Depressed participants also exhibited an increased LPP to negative stimuli compared to positive or neutral stimuli. Together, these two studies suggest that depression is characterized by relatively increased sensitivity to affective self-relevant stimuli, perhaps in the context of a broader reduction in emotional reactivity to stimuli that are not self-relevant. Thus, depression may be characterized by a more nuanced pattern based on the degree of stimulus self-relevance than either a global decrease or increase in reactivity to affective stimuli.

Detection of sarcastic speech: The role of the right hemisphere in ambiguity resolution.

Two experiments were conducted to determine if the right hemisphere (RH) plays a central role in understanding sarcasm. In Experiment 1, 48 participants completed a target detection task using dichotically presented phrases that were sincere (message compatible), sarcastic (conflicting semantic and prosodic message), or neutral (no emotional prosody). Sarcastic phrases presented to the left ear (LE)/RH produced faster response times than sarcastic phrases presented to the right ear/left hemisphere. Accuracy results indicated an overall LE/RH advantage for detecting both sarcastic and sincere phrases. Experiment 2 utilized the same task with the addition of event-related potential recording. There was a reliable N400 seen in response to the sarcastic phrases, but only with LE/RH presentation. These results suggest that the RH is particularly sensitive to the mismatch between semantic and prosodic information characterized by sarcasm.

Pragmatic inferences modulate N400 during sentence comprehension: evidence from picture-sentence verification.

The present study examines the online realization of pragmatic meaning using event-related potentials (ERPs). Participants read sentences including the English quantifier some, which has both a semantic meaning (at least one) and a pragmatic meaning (not all). Unlike previous ERP studies of this phenomenon, sentences in the current study were evaluated not in terms of their truth with respect to the real world, but in terms of their consistency with a picture presented before the sentence. Sentences (such as "The boy cut some of the steaks in this story") were constructed such that either (1) both the semantic and pragmatic interpretations were true with respect to the preceding picture (when the boy in fact cut some but not all of the steaks); (2) neither interpretation was true (when the boy in fact cut none of the steaks); or (3) the semantic interpretation was true but the pragmatic interpretation false (when the boy in fact cut all of the steaks). ERPs at the object word, which determined whether the sentence was consistent with the story, showed the largest N400 effect for objects that made the sentence false, whereas they showed an intermediate effect for objects that made the sentence false under the pragmatic interpretation but true under the semantic interpretation. The results suggest that this pragmatic aspect of meaning is computed online and integrated into the sentence model rapidly enough to influence comprehension of later words.

Depression reduces perceptual sensitivity for positive words and pictures.

There is evidence of maladaptive attentional biases for lexical information (e.g., Atchley, Ilardi, & Enloe, 2003; Atchley, Stringer, Mathias, Ilardi, & Minatrea, 2007) and for pictographic stimuli (e.g., Gotlib, Krasnoperova, Yue, & Joormann, 2004) among patients with depression. The current research looks for depressotypic processing biases among depressed out-patients and non-clinical controls, using both verbal and pictorial stimuli. A d' measure (sensitivity index) was used to examine each participant's perceptual sensitivity threshold. Never-depressed controls evidenced a detection bias for positive picture stimuli, while depressed participants had no such bias. With verbal stimuli, depressed individuals showed specific decrements in the detection of positive person-referent words (WINNER), but not with positive non-person-referent words (SUNSHINE) or with negative words. Never-depressed participants showed no such differences across word types. In the current study, depression is characterised both by an absence of the normal positivistic biases seen in individuals without mood disorders (consistent with McCabe & Gotlib, 1995), and by a specific reduction in sensitivity for person-referent positive information that might be inconsistent with depressotypic self-schemas.

Examining lateralized lexical ambiguity processing using dichotic and cross-modal tasks.

The individual roles played by the cerebral hemispheres during the process of language comprehension have been extensively studied in tasks that require individuals to read text (for review see Jung-Beeman, 2005). However, it is not clear whether or not some aspects of the theorized laterality models of semantic comprehension are a result of the modality of presentation. Extending earlier work examining lateralized semantic processing using lexically ambiguous words, the current experiments utilized two modified lexical-decision tasks (one fully auditory and one cross-modal) with dichotically presented target stimuli. When targets were presented to the right ear/left hemisphere there was a distinct advantage for detecting words that are associated with the dominant meaning of the ambiguous word over the subordinate meaning. In contrast, for left ear/right hemisphere trials, there was either no difference between the pattern of semantic access for dominant and subordinate meaning (dichotic only) or a processing advantage for the subordinate meaning of the ambiguous word (with cross-modal presentation). These data suggest that the complimentary hemispheric strategies that allow for semantic access are not modality specific and instead characterize how the hemispheres each contribute to comprehension for both speech and text. Thus, dichotic presentation does seem to allow for the study of subtle hemispheric difference in meaning comprehension.

What Habituates in Infant Visual Habituation? A Psychophysiological Analysis.

Despite the use of visual habituation over the past half century, relatively little is known about its underlying processes. We analyzed heart rate (HR) taken simultaneous with looking during infant-controlled habituation sessions collected longitudinally at 4, 6, and 8 months of age with the goal of examining how HR and HR-defined phases of attention change across habituation. There were four major findings. First, the depth and topography of decelerations and proportion of sustained attention (SA) did not vary across habituation at any age, which suggested (in contrast to the tenets of comparator theory) the persistence of substantial cognitive activity at the end of visual habituation. Second, attention termination (AT) robustly declined across trials, suggesting that, contrary to prior thinking, AT might be a sensitive indicant of visual learning. Third, infants at all ages showed an HR increase (startle) to stimulus onset on the first trial, the magnitude of which was associated with subsequent delayed HR deceleration and less SA; thus, stimulus events affect processing during trials. Finally, mean overall HR reliably increased across trials for all ages. This last finding implies the need to distinguish between "phasic" HR changes (e.g., decelerations during looks) and longer term "tonic" HR changes (mean increases across trials) during habituation, and raises the question of what processes the tonic increases might reflect within the habituation paradigm.

Gray matter volume differences and the effects of smoking on gray matter in schizophrenia.

OBJECTIVE: Many studies have evaluated differences in gray matter volume in schizophrenia, but have not considered the possible effects of smoking, which is extraordinarily common in people with the illness. The present study used voxel-based morphometry (VBM) to examine differences in gray matter in subjects with schizophrenia and evaluate the effects of smoking on this measure. METHODS: Thirty-two subjects with schizophrenia (14 smokers, 18 non-smokers) and 32 healthy comparison subjects participated in the study. Whole brain, voxel-wise analyses of regional gray matter volume were conducted using voxel-based morphometry (VBM). RESULTS: Reduced gray matter was observed in the schizophrenia group in the orbitofrontal cortex, bilateral insula and superior temporal gyri (STG), bilateral dorsolateral prefrontal cortices (DLPFC), medial frontal gyrus, and cingulate gyrus. Within this group, smoking subjects had greater lateral prefrontal and STG gray matter volumes relative to non-smoking subjects. CONCLUSIONS: The finding of reduced gray matter volume in prefrontal and temporal regions in schizophrenia is consistent with prior anatomical tracing and whole-brain voxel-based studies. Greater gray matter volumes in smoking relative to non-smoking subjects with schizophrenia highlight a potential experimental confound in volumetric studies and suggests that smoking may be associated with a relative preservation of lateral prefrontal and temporal gray matter in schizophrenia.

Increased hemodynamic response in the hippocampus, thalamus and prefrontal cortex during abnormal sensory gating in schizophrenia.

OBJECTIVE: Deficits in sensory gating are a common feature of schizophrenia. Failure of inhibitory gating mechanisms, shown by poor suppression of evoked responses to repeated auditory stimuli, has been previously studied using EEG methods. These methods yield information about the temporal characteristics of sensory gating deficits, but do not identify brain regions involved in the process. Hence, the neuroanatomical substrates of poor sensory gating in schizophrenia remain largely unknown. This study used functional magnetic resonance imaging (fMRI) to investigate the functional neuroanatomy of sensory gating deficits in schizophrenia. METHODS: Twelve patients with schizophrenia and 12 healthy comparison subjects were scanned at 3 Tesla while performing a sensory gating task developed for fMRI. P50 EEG evoked potential recordings from a paired-stimulus conditioning-test paradigm were obtained from the same subjects. RESULTS: Compared to healthy comparison subjects, patients with schizophrenia exhibited greater activation in the hippocampus, thalamus, and dorsolateral prefrontal cortex (DLPFC) during the fMRI sensory gating task. No group difference was observed in the superior temporal gyrus. Schizophrenia subjects also showed decreased P50 suppression as measured with EEG. Hemodynamic response in the fMRI measure was positively correlated with test/conditioning ratios from the EEG sensory gating measure. CONCLUSIONS: Poor sensory gating in schizophrenia is associated with dysfunction of an apparent network of brain regions, including the hippocampus, thalamus and DLPFC. Greater activation of these regions is consistent with evidence for diminished inhibitory function in schizophrenia.