Johanna Kissler

Event related potentials to emotional adjectives during reading

We investigated to what extent emotional connotation influences cortical potentials during reading. To this end, event-related potentials (ERPs) were recorded during reading of high arousal pleasant and unpleasant and low arousal neutral adjectives that were presented at rates of 1 Hz and 3 Hz. Enhanced processing of both pleasant and unpleasant emotional compared to neutral adjectives was first reflected in an amplified early posterior negativity (EPN) starting from 200 ms after word onset. Later potentials (>300 ms), as analyzed in the slower 1 Hz condition, revealed facilitated processing selectively for pleasant adjectives that were associated with a reduced N400 and an enhanced late positive potential (LPP). Pleasant adjectives were also better remembered in an incidental memory test. Thus, emotionally relevant adjectives are processed spontaneously and selectively. Initially, emotional arousal drives attention capture (EPN). Healthy subjects may have a natural bias toward pleasant information facilitating late ERPs (N400, LPP) to pleasant adjectives as well as their superior recall.

Emotion and attention in visual word processing—An ERP study

Emotional words are preferentially processed during silent reading. Here, we investigate to what extent different components of the visual evoked potential, namely the P1, N1, the early posterior negativity (EPN, around 250 ms after word onset) as well as the late positive complex (LPC, around 500 ms) respond differentially to emotional words and whether this response depends on the availability of attentional resources. Subjects viewed random sequences of pleasant, neutral and unpleasant adjectives and nouns. They were first instructed to simply read the words and then to count either adjectives or nouns. No consistent effects emerged for the P1 and N1. However, during both reading and counting the EPN was enhanced for emotionally arousing words (pleasant and unpleasant), regardless of whether the word belonged to a target or a non-target category. A task effect on the EPN was restricted to adjectives, but the effect did not interact with emotional content. The later centro-parietal LPC (450-650 ms) showed a large enhancement for the attended word class. A small and topographically distinct emotion-LPC effect was found specifically in response to pleasant words, both during silent reading and the active task. Thus, emotional word content is processed effortlessly and automatically and is not subject to interference from a primary grammatical decision task. The results are in line with other reports of early automatic semantic processing as reflected by posterior negativities in the ERP around 250 ms after word onset. Implications for models of emotion-attention interactions in the brain are discussed.

Cerebral pathways in processing of affective prosody: A dynamic causal modeling study

This study was conducted to investigate the connectivity architecture of neural structures involved in processing of emotional speech melody (prosody). 24 subjects underwent event-related functional magnetic resonance imaging (fMRI) while rating the emotional valence of either prosody or semantics of binaurally presented adjectives. Conventional analysis of fMRI data revealed activation within the right posterior middle temporal gyrus and bilateral inferior frontal cortex during evaluation of affective prosody and left temporal pole, orbitofrontal, and medial superior frontal cortex during judgment of affective semantics. Dynamic causal modeling (DCM) in combination with Bayes factors was used to compare competing neurophysiological models with different intrinsic connectivity structures and input regions within the network of brain regions underlying comprehension of affective prosody. Comparison on group level revealed superiority of a model in which the right temporal cortex serves as input region as compared to models in which one of the frontal areas is assumed to receive external inputs. Moreover, models with parallel information conductance from the right temporal cortex were superior to models in which the two frontal lobes accomplish serial processing steps. In conclusion, connectivity analysis supports the view that evaluation of affective prosody requires prior analysis of acoustic features within the temporal and that transfer of information from the temporal cortex to the frontal lobes occurs via parallel pathways.

Amygdala activation during reading of emotional adjectives—an advantage for pleasant content

This event-related functional magnetic resonance imaging (fMRI) study investigated brain activity elicited by emotional adjectives during silent reading without specific processing instructions. Fifteen healthy volunteers were asked to read a set of randomly presented high-arousing emotional (pleasant and unpleasant) and low-arousing neutral adjectives. Silent reading of emotional in contrast to neutral adjectives evoked enhanced activations in visual, limbic and prefrontal brain regions. In particular, reading pleasant adjectives produced a more robust activation pattern in the left amygdala and the left extrastriate visual cortex than did reading unpleasant or neutral adjectives. Moreover, extrastriate visual cortex and amygdala activity were significantly correlated during reading of pleasant adjectives. Furthermore, pleasant adjectives were better remembered than unpleasant and neutral adjectives in a surprise free recall test conducted after scanning. Thus, visual processing was biased towards pleasant words and involved the amygdala, underscoring recent theoretical views of a general role of the human amygdala in relevance detection for both pleasant and unpleasant stimuli. Results indicate preferential processing of pleasant information in healthy young adults and can be accounted for within the framework of appraisal theory.

MEG gamma band activity in schizophrenia patients and healthy subjects in a mental arithmetic task and at rest.

OBJECTIVES High frequency oscillations have been suggested as a correlate of cognitive processes and have recently also been implicated in aberrant forms of information processing. The present study investigated whether magnetoencephalographic (MEG) gamma band activity (20-71 Hz) can serve as an index of cognitive processes in the absence of external stimulation and to what extent gamma activity differs between healthy people and schizophrenia patients. METHODS The amount and topography of MEG power in the gamma band range was examined in 15 schizophrenia patients and 15 healthy comparison subjects while performing a complex mental arithmetic task and at rest. RESULTS In healthy subjects a left frontal and left fronto-temporal increase in gamma power was observed during mental arithmetic. Schizophrenia patients either failed to display such a task effect (30-45 Hz) or had reversed lateralization with enhanced activity over right frontal and right fronto-temporal regions under cognitive demands (45-71 Hz). In the frequency band from 60 to 71 Hz patients showed less gamma at fronto-temporal, posterio-temporal and occipital sites irrespective of the task. CONCLUSIONS These results indicate, first, that gamma topography can index cognitive activation in a very complex and purely internal task. Second, groups differed in the pattern of activation during the task, a result which may be consistent with working memory dysfunction in schizophrenia. Third, the general topographic difference between healthy subjects and patients is in line with the notion of abnormalities in the thalamocortical circuit in schizophrenia.

Source distribution of neuromagnetic slow waves and MEG-delta activity in schizophrenic patients

BACKGROUND Schizophrenic patients exhibit more activity in the electroencephalographic delta and theta frequency range than do control subjects. Using magnetic source imaging (MSI) our study aimed to explore this phenomenon in the magnetoencephalogram (MEG), the distribution of its sources, and associations between symptom profiles and sources of low-frequency activity in the brain. METHODS Whole-head MEG recordings were obtained from 28 schizophrenic patients and 20 healthy control subjects during a resting condition. The generators of the focal magnetic slow waves were located employing a single moving dipole model. Distributed or multiple delta and theta sources were captured by the minimum norm estimate. RESULTS Both localization procedures showed slow wave activity to be enhanced in schizophrenic patients compared with control subjects. Focal slow wave activity differed most between groups in frontotemporal and in posterior regions. Slow wave activity was associated with symptom characteristics in that positive symptoms varied with frontal delta and theta activity. CONCLUSIONS Results indicate that activity in low-frequency bands in schizophrenic patients exceeds the activity of control subjects in distinct areas, and that this focal clustering of neuromagnetic slow waves may be related to psychopathologic characteristics.

Electroencephalography/magnetoencephalography study of cortical activities preceding prosaccades and antisaccades

The temporal and spatial characteristics of brain activity preceding prosaccades and antisaccades were investigated using source reconstructions of 64-channel electroencephalography and 148-channel magnetoencephalography data. Stimulus-locked data showed early cuneus activity was stronger during antisaccades, and later occipital gyrus activity was stronger preceding prosaccades, which suggests a top-down influence on early visual processing. Response-locked data showed that supplementary eye field, prefrontal cortex, and medial frontal eye field activity was greater for antisaccades than for prosaccades prior to saccade generation. Lateral frontal eye field activity appeared to be inhibited prior to antisaccade response generation. The spatial and temporal resolution of combined electroencephalography/magnetoencephalography data allows the evaluation of specific cortical activities preceding saccades and for demonstration of how activities differ as a function of response contingencies.

Source distribution of neuromagnetic slow wave activity in schizophrenic and depressive patients

OBJECTIVE Focal slow waves in the delta and theta frequency range frequently appear in psychopathological conditions. Due to their focal nature they can be localized by dipole modeling. We previously reported regional clustering of slow waves in temporal and parietal cortex of schizophrenic patients whereas such activity is largely absent in normals. Here we examine, to what extent distribution of slow wave generators differentiates schizophrenic from depressive syndromes. METHODS The regional densities of generators of focal slow waves were determined during resting conditions in patients with DSM-IV diagnoses of schizophrenia (N=25) and depression (N=27) and in 18 healthy controls. RESULTS Schizophrenic patients demonstrated accentuated temporal and parietal delta and theta dipole clustering, when compared to both the control and the depressive sample. In contrast, depressive patients had reduced frontal and prefrontal delta and theta dipole density relative to both schizophrenics and controls. This pattern was not related to age. Men generally displayed somewhat higher slow wave activity than women. For the areas of most pronounced slow wave deviances activity within each group was related to symptom scores: higher left-temporal slow wave activity was associated with hallucinations in schizophrenics, suppression of left-prefrontal slow wave activity correlated with depression scores. CONCLUSIONS Results suggest that slow wave distribution may assist in differentially diagnosing psychopathological conditions.

Source distribution of neuromagnetic slow-wave activity in schizophrenic patients—effects of activation

When slow waves in the EEG delta and theta frequency range appear in the waking state, they may indicate pathological conditions including psychopathology. The generators of focal slow waves can be mapped using magnetic source imaging. The resulting brain maps may possibly characterize dysfunctional brain areas. The present study examined the stability of the density and distribution of MEG slow waves during three conditions-rest, mental arithmetic and imagery-in 30 schizophrenic patients and 17 healthy controls. Schizophrenic patients displayed a higher density of delta and theta generators primarily in temporal and parietal areas. The group difference was not affected by the particular conditions. The focal concentration of delta and theta slow waves did not differ between patients with and without neuroleptic medication, whereas the prominence of theta dipoles in the temporal area correlated with neuroleptic dosage. The relative amount of temporal slow waves was correlated with the negative symptoms score (PANSS-N) suggesting that temporal dysfunction may be related to negative symptomatology.Results suggest that the distribution of slow-wave activity, measured in a standardized setting, might add diagnostic information about brain abnormalities in schizophrenia.

Shaping Memory Accuracy by Left Prefrontal Transcranial Direct Current Stimulation

Human memory is dynamic and flexible but is also susceptible to distortions arising from adaptive as well as pathological processes. Both accurate and false memory formation require executive control that is critically mediated by the left prefrontal cortex (PFC). Transcranial direct current stimulation (tDCS) enables noninvasive modulation of cortical activity and associated behavior. The present study reports that tDCS applied to the left dorsolateral PFC (dlPFC) shaped accuracy of episodic memory via polaritiy-specific modulation of false recognition. When applied during encoding of pictures, anodal tDCS increased whereas cathodal stimulation reduced the number of false alarms to lure pictures in subsequent recognition memory testing. These data suggest that the enhancement of excitability in the dlPFC by anodal tDCS can be associated with blurred detail memory. In contrast, activity-reducing cathodal tDCS apparently acted as a noise filter inhibiting the development of imprecise memory traces and reducing the false memory rate. Consistently, the largest effect was found in the most active condition (i.e., for stimuli cued to be remembered). This first evidence for a polarity-specific, activity-dependent effect of tDCS on false memory opens new vistas for the understanding and potential treatment of disturbed memory control.