Hauswald, Anne
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What it means to be Zen : Marked modulations of local and interareal synchronization during open monitoring meditation
Experienced meditators are able to voluntarily modulate their state of consciousness and attention. In the present study, we took advantage of this ability and studied brain activity related to the shift of mental state. Electrophysiological activity, i.e. EEG, was recorded from 11 subjects with varying degrees of meditation experience during Zen meditation (a form of open monitoring meditation) and during non-meditation rest. On a behavioral level, mindfulness scores were assessed using the Mindfulness Attention and Awareness Scale (MAAS). Analysis of EEG source power revealed the so far unreported finding that MAAS scores significantly correlated with gamma power (30–250 Hz), particularly high-frequency gamma (100–245 Hz), during meditation. High levels of mindfulness were related to increased high-frequency gamma, for example, in the cingulate cortex and somatosensory cortices. Further, we analyzed the relationship between connectivity during meditation and self-reported mindfulness (MAAS). We found a correlation between graph measures in the 160–170 Hz range and MAAS scores. Higher levels of mindfulness were related to lower small worldedness as well as global and local clustering in paracentral, insular, and thalamic regions during meditation. In sum, the present study shows significant relationships of mindfulness and brain activity during meditation indicated by measures of oscillatory power and graph theoretical measures. The most prominent effects occur in brain structures crucially involved in processes of awareness and attention, which also show structural changes in short- and long-term meditators, suggesting continuative alterations in the meditating brain. Overall, our study reveals strong changes in ongoing oscillatory activity as well as connectivity patterns that appear to be sensitive to the psychological state changes induced by Zen meditation.
ERP dynamics underlying successful directed forgetting of neutral but not negative pictures
Subjective experience suggests that negatively arousing memories are harder to control than neutral ones. Here, we investigate this issue in an item-cued directed forgetting experiment. Electroencephalogram event-related potentials (ERPs) were recorded as participants viewed un-arousing neutral and highly arousing negative photographs, each followed by a cue to remember or forget it. Directed forgetting, that is reduced recognition of ‘to-be-forgotten’ items, occurred for neutral but not negative pictures. ERPs revealed three underlying effects: first, during picture viewing a late parietal positive potential (LPP) was more pronounced for negative than for neutral pictures. Second, ‘remember’ cues were associated with larger LPPs than ‘forget’ cues. Third, an enhanced frontal positivity appeared for ‘forget’ cues. This frontal positivity was generated in right dorso-lateral prefrontal regions following neutral pictures and in medial frontal cortex following negative pictures. LPP magnitude when viewing negative pictures was correlated with reduced directed forgetting, whereas both the enhanced frontal positivity for forget cues and the larger parietal positivity for remember cues predicted more directed forgetting. This study indicates that both processes of selective rehearsal (parietal positivities) and frontally controlled inhibition contribute to successful directed forgetting. However, due to their deeper incidental processing, highly arousing negative pictures are exempt from directed forgetting.
Directed forgetting of emotional material : cognitive and neural mechanisms
Directed forgetting refers to people s ability to intentionally forget material designated as unimportant. Two paradigms are usually used to explore this ability: The item and the list method. In the item method, stimuli are presented individually, each followed by an instruction to forget or remember the previous item. In the list method, two lists of stimuli are presented. The first list is either followed by a forget instruction or a remember instruction. Memory is tested for all items regardless of initial instruction. Directed forgetting occurs as reduced recall of to-be-forgotten compared to to-be-remembered stimuli in the item method and as reduced recall of the to-be-forgotten first list compared to a to-be-remembered first list. Although directed forgetting paradigms have been used widely, some important issues have been neglected and are less well understood: (1) Is directed forgetting material-specific? (2) Is directed forgetting modulated by emotional material? (3) What are the electrophysiological dynamics of directed forgetting?
Six experiments will be presented, aiming at answering these questions. Two experiments (chapter 1) investigated item method directed forgetting of complex colorful pictures. Directed forgetting has been shown with verbal material, but no previous study explored item method directed forgetting of complex and colorful pictures. Exp. 1 investigated item method directed forgetting of neutral complex pictures. Further, exp. 2 focused on behavioral and electrophysiological effects of item method directed forgetting of neutral compared to unpleasant complex pictures.
Four experiments (chapter 2) explored list method directed forgetting of words varying in emotional content. Although there are several studies on list method directed forgetting of emotional material, the findings are inconclusive as systematic investigations on healthy participants are missing. Thus, list emotionality was systematically varied in experiments 1-4 exploring the influence of emotion on directed forgetting. In exp. 1, both lists comprised neutral words and unpleasant words in experiment 2. In exp. 3, the first list consisted of neutral words and the second list of unpleasant words, while in exp. 4, the assignment was vice versa. Electrophysiological measures were assessed in all four experiments.
The experiments of chapter 1 found item method directed forgetting for neutral but not for unpleasant pictures. Successful forgetting of neutral pictures was related to enhanced electrophysiological positivity in frontal regions, which occurred during encoding of the forget instruction following neutral pictures. The lack of directed forgetting for unpleasant pictures was associated with late positivities reflecting enhanced encoding already during picture presentation and less frontal positivity during encoding of the forget instruction for unpleasant pictures. Further, regardless of previous picture valence, remember instructions evoked late positivities, which have been related to enhanced encoding processes.
In all experiments on list method directed forgetting, directed forgetting was found regardless of list emotionality. Moreover, memory effects of context change occurred, when the emotional content was changed between the first and the second list (exp. 3 and 4). Electrophysiologically, increased activity was found during the presentation of words that followed forget instructions compared to words following remember instructions. This activity difference occurred as late positivities, which have been associated with encoding and attentional processes.
These findings provide new insights for the above raised questions: (1) Directed forgetting is not restricted to verbal material but also occurs for complex neutral pictures. (2) Directed forgetting occurs for emotional and neutral words equally, while complex pictures depicting unpleasant content are exempt of directed forgetting. (3) The EEG data suggest that successful item method directed forgetting is associated with late positivities during remember instructions and frontal activity enhancement during forget instructions. In list method directed forgetting, late positivities occurred following the forget instruction.
Thus, the findings support a two-factor for both the item and the list method: Processes of selective rehearsal and inhibition can explain item method directed forgetting. Late positivities, which are associated with enhanced encoding, indicate selective rehearsal. These potentials occurred during presentation of unpleasant pictures and of remember instructions. Inhibitory processes are suggested by frontal positivities during forget instructions, which were particularly enhanced following neutral pictures. List method directed forgetting can be explained by attentional focusing, which is supported by the occurrence of late positivities after the forget instruction, and by memory effects of context change.
MEG premotor abnormalities in children with Asperger's syndrome : Determinants of social behavior?
Children with Asperger's syndrome show deficits in social functioning while their intellectual and language development is intact suggesting a specific dysfunction in mechanisms mediating social cognition. An action observation/execution matching system might be one such mechanism. Recent studies indeed showed that electrophysiological modulation of the “Mu-rhythm” in the 10–12 Hz range is weaker when individuals with Asperger's syndrome observe actions performed by others compared to controls. However, electrophysiological studies typically fall short in revealing the neural generators of this activity. To fill this gap we assessed magnetoencephalographic Mu-modulations in Asperger's and typically developed children, while observing grasping movements. Mu-power increased at frontal and central sensors during movement observation. This modulation was stronger in typical than in Asperger children. Source localization revealed stronger sources in premotor cortex, the intraparietal lobule (IPL) and the mid-occipito-temporal gyrus (MOTG) and weaker sources in prefrontal cortex in typical participants compared to Asperger. Activity in premotor regions, IPL and MOTG correlated positively with social competence, whereas prefrontal Mu-sources correlated negatively with social competence. No correlation with intellectual ability was found at any of these sites. These findings localize abnormal Mu-activity in the brain of Asperger children providing evidence which associates motor-system abnormalities with social-function deficits.
Selective forgetting and remembering of emotional and neutral stimuli - ERP evidence from item method directed forgetting
Directed forgetting of complex pictures in an item method paradigm
An item-cued directed forgetting paradigm was used to investigate the ability to control episodic memory and selectively encode complex coloured pictures. A series of photographs was presented to 21 participants who were instructed to either remember or forget each picture after it was presented. Memory performance was later tested with a recognition task where all presented items had to be retrieved, regardless of the initial instructions. A directed forgetting effect that is, better recognition of "to-be-remembered" than of "to-be-forgotten" pictures was observed, although its size was smaller than previously reported for words or line drawings. The magnitude of the directed forgetting effect correlated negatively with participants' depression and dissociation scores. The results indicate that, at least in an item method, directed forgetting occurs for complex pictures as well as words and simple line drawings. Furthermore, people with higher levels of dissociative or depressive symptoms exhibit altered memory encoding patterns.
Memory control in post-traumatic stress disorder : evidence from item method directed forgetting in civil war victims in Northern Uganda
Background Traumatized individuals and particularly post-traumatic stress disorder (PTSD) patients are characterized by memory disturbances that suggest altered memory control. The present study investigated the issue using an item method, directed forgetting (DF) paradigm in 51 civil war victims in Uganda. All participants had been exposed to severe traumatic stress and 26 additionally suffered from PTSD.
Method In an item cued, DF paradigm photographs were presented, each followed by an instruction to either remember or forget it. A recognition test for all initially presented photographs and thematically similar distracters followed. DF patterns were compared between the non-PTSD and the PTSD groups. Post-experimental ratings of picture valence and arousal were collected and correlated with DF.
Results Results revealed DF, that is, reduced recognition for ‘to-be-forgotten’ items in the non-PTSD but not in the PTSD group. Moreover, in the non-PTSD, but not in the PTSD group, false alarms were reduced for ‘to-be-remembered’ items. Finally, DF was reduced in those participants who rated the pictures as more arousing, the PTSD group giving, on average, higher arousal ratings.
Conclusions Data indicate that DF is reduced in PTSD and that the reduction is related to stimulus arousal. Furthermore, individuals with PTSD are characterized by a more global encoding style than individuals without PTSD, reflected in a higher false alarm rate. In sum, traumatized individuals with (but not without) PTSD are impaired in their ability to selectively control episodic memory encoding. This impairment may contribute to clinical features of the disorder such as intrusions and flashbacks.
Neuromagnetic Activity During Recognition of Emotional Pictures
Recently studied old stimuli lead to larger frontal and parietal ERP responses than new stimuli. The present experiment investigated the neuromagnetic correlates (MEG) of this old-new effect and its modulation by emotional stimulus content. Highly arousing pleasant, highly arousing unpleasant and un-arousing neutral photographs were presented to the participants with the instruction to memorize them. They were later re-presented together with new photographs in an old-new decision task. In line with previous ERP studies, a long-lasting old-new effect (350 700 ms) was found. Independently, an emotion effect also occurred, as reflected in a, particularly left temporal, activity increase for emotional pictures between 450 and 580 ms. Moreover, only for the pleasant pictures did the early part of the old-new effect, which is thought to reflect familiarity based recognition processes, interact with picture content: The old-new effect for pleasant pictures in frontal regions was larger than the one for neutral or unpleasant pictures between 350 and 450 ms. In parallel, subjects responses were accelerated towards and biased in favour of classifying pleasant pictures as old. However, when false alarm rate was taken into account, there was no significant effect of emotional content on recognition accuracy. In sum, this MEG study demonstrates an effect of particularly pleasant emotional content on recognition memory which may be mediated by a familiarity based process.
Das Wiedererkennen emotionaler Bilder : eine MEG-Studie
According to an evolutionary perspective, it seems very reasonable that emotionally relevant events hold an exceptional and privileged position in memory. Surviving and reproduction are the fundamental factors within such a theory. Most behaviour can be reduced to those factors as one reach an attractive source or withdraw from an aversive one. Essentially for fast and efficient dealing with e.g. threatening situations are a quick interpretation of the danger and a preferential processing of associated aspects. Therefore a modulating influence of emotion on recognition is of huge relevance for the ability to act adaptively.
Because of its adaptive relevance the interplay of emotion and memory is of interest. So far mainly behavioural and electrophysiological experiments were done. Those studies indicate a modulating effect of emotion on recognition. However, the operating mode of this connection is still unclear. The goal of this study is therefore to contribute to the understanding of the interaction of emotion and memory.
In this experiment the effects of visual stimuli of different emotional categories on recognition performance was investigated. Therefore neuromagnetic brain activity was recorded using MEG. Highly arousing pleasant and unpleasant as well as neutral pictures were presented for memorizing. Subsequently these pictures were presented again together with similar new pictures. Participants were instructed to indicate if pictures were old or new. Neuromagnetic activity was recorded during both the encoding and the recall phase. Thereby the emotion effect as well as the old-new effect for emotional items could be examined.
During encoding increased frontal activity starting around 300 ms after picture onset was observed particularly for pleasant pictures. For the recognition phase, the data show a frontal interaction of emotion and repetition starting from 300ms. Initially, this interaction was mainly produced by the recognition of old pleasant pictures leading to stronger cortical activity. Later, recognition of both pleasant and unpleasant old pictures leads to an increase in frontal brain activity. Behavioural data parallel this pattern in that both pleasant and unpleasant pictures were recognized more accurately and pleasant pictures only also faster than neutral pictures.
These findings are consistent with other data demonstrating an important role of the frontal cortex in both memory and emotion.