Face Processing in Developmental Prosopagnosia: Altered Neural Representations in the Fusiform Face Area.

Rationale: Face expertise is a pivotal social skill. Developmental prosopagnosia (DP), i.e., the inability to recognize faces without a history of brain damage, affects about 2% of the general population, and is a renowned model system of the face-processing network. Within this network, the right Fusiform Face Area (FFA), is particularly involved in face identity processing and may therefore be a key element in DP. Neural representations within the FFA have been examined with Representational Similarity Analysis (RSA), a data-analytical framework in which multi-unit measures of brain activity are assessed with correlation analysis. Objectives: Our study intended to scrutinize modifications of FFA-activation during face encoding and maintenance based on RSA. Methods: Thirteen participants with DP (23-70 years) and 12 healthy control subjects (19-62 years) participated in a functional MRI study, including morphological MRI, a functional FFA-localizer and a modified Sternberg paradigm probing face memory encoding and maintenance. Memory maintenance of one, two, or four faces represented low, medium, and high memory load. We examined conventional activation differences in response to working memory load and applied RSA to compute individual correlation-matrices on the voxel level. Group correlation-matrices were compared via Donsker's random walk analysis. Results: On the functional level, increased memory load entailed both a higher absolute FFA-activation level and a higher degree of correlation between activated voxels. Both aspects were deficient in DP. Interestingly, control participants showed a homogeneous degree of correlation for successful trials during the experiment. In DP-participants, correlation levels between FFA-voxels were significantly lower and were less sustained during the experiment. In behavioral terms, DP-participants performed poorer and had longer reaction times in relation to DP-severity. Furthermore, correlation levels were negatively correlated with reaction times for the most demanding high load condition. Conclusion: We suggest that participants with DP fail to generate robust and maintained neural representations in the FFA during face encoding and maintenance, in line with poorer task performance and prolonged reaction times. In DP, alterations of neural coding in the FFA might therefore explain curtailing in working memory and contribute to impaired long-term memory and mental imagery.

Visuospatial computer game play after memory reminder delivered three days after a traumatic film reduces the number of intrusive memories of the experimental trauma.

OBJECTIVE: The experience of intrusive memories is a core clinical symptom of posttraumatic stress disorder (PTSD), and can be distressing in its own right. Notions of dual task interference and reconsolidation-update mechanisms suggest novel approaches to target intrusive memories. This study tested the hypothesis that a single-session cognitive intervention (memory reminder task plus Tetris gameplay) would reduce the occurrence of experimental trauma memories even when delivered 3 days post-trauma. Critically, this study tested effects against two control groups: Reminder-only, and reminder plus another computer game (a form of Quiz). METHODS: 86 healthy volunteers (59% female, age M = 24.35, SD = 4.59 years) watched a trauma film and then recorded their intrusive memories in a diary for 3 days (pre-intervention). They then returned to the lab. After presentation of visual reminder cues for the film plus a 10 min wait period (memory reminder task), participants were randomized into one of three task conditions (Tetris game play, Quiz game play, vs. reminder-only). They then kept the diary for a further 3 days (post-intervention). RESULTS: As predicted, after the experimental manipulation, the reminder + Tetris group experienced significantly fewer intrusions than the reminder-only group (d = 1.37). Further, the reminder + Tetris group also experienced significantly fewer intrusions than the reminder + Quiz (d = 0.65) group. Contrary to predictions, the reminder + Quiz group experienced significantly fewer intrusions than the reminder-only group (d = 0.69). Prior to the experimental manipulation, there was no significant difference between groups in number of intrusions. Recognition memory test scores for facts of the trauma film after 6 days were comparable between groups. CONCLUSIONS: We demonstrated that 3 days after experimental trauma (i.e. after memory consolidation) an intervention comprising a reminder task prior to a 15 min cognitive interference task (one of two computer games) led to a reduction in intrusion occurrence compared to reminder only. We interpret and discuss our findings within the framework of supposed reconsolidation-update mechanisms and competition for limited (visuospatial) working memory resources. Should these effects hold true in clinical populations, this type of simple intervention approach could help contribute to reducing intrusive memories of trauma.

Audiovisual integration supports face-name associative memory formation.

Prior multisensory experience influences how we perceive our environment, and hence how memories are encoded for subsequent retrieval. This study investigated if audiovisual (AV) integration and associative memory formation rely on overlapping or distinct processes. Our functional magnetic resonance imaging results demonstrate that the neural mechanisms underlying AV integration and associative memory overlap substantially. In particular, activity in anterior superior temporal sulcus (STS) is increased during AV integration and also determines the success of novel AV face-name association formation. Dynamic causal modeling results further demonstrate how the anterior STS interacts with the associative memory system to facilitate successful memory formation for AV face-name associations. Specifically, the connection of fusiform gyrus to anterior STS is enhanced while the reverse connection is reduced when participants subsequently remembered both face and name. Collectively, our results demonstrate how multisensory associative memories can be formed for subsequent retrieval.

Intracranial electroencephalography power and phase synchronization changes during monaural and binaural beat stimulation.

Auditory stimulation with monaural or binaural auditory beats (i.e. sine waves with nearby frequencies presented either to both ears or to each ear separately) represents a non-invasive approach to influence electrical brain activity. It is still unclear exactly which brain sites are affected by beat stimulation. In particular, an impact of beat stimulation on mediotemporal brain areas could possibly provide new options for memory enhancement or seizure control. Therefore, we examined how electroencephalography (EEG) power and phase synchronization are modulated by auditory stimulation with beat frequencies corresponding to dominant EEG rhythms based on intracranial recordings in presurgical epilepsy patients. Monaural and binaural beat stimuli with beat frequencies of 5, 10, 40 and 80 Hz and non-superposed control signals were administered with low amplitudes (60 dB SPL) and for short durations (5 s). EEG power was intracranially recorded from mediotemporal, temporo-basal and temporo-lateral and surface sites. Evoked and total EEG power and phase synchronization during beat vs. control stimulation were compared by the use of Bonferroni-corrected non-parametric label-permutation tests. We found that power and phase synchronization were significantly modulated by beat stimulation not only at temporo-basal, temporo-lateral and surface sites, but also at mediotemporal sites. Generally, more significant decreases than increases were observed. The most prominent power increases were seen after stimulation with monaural 40-Hz beats. The most pronounced power and synchronization decreases resulted from stimulation with monaural 5-Hz and binaural 80-Hz beats. Our results suggest that beat stimulation offers a non-invasive approach for the modulation of intracranial EEG characteristics.

Neural communication patterns underlying conflict detection, resolution, and adaptation.

In an ever-changing environment, selecting appropriate responses in conflicting situations is essential for biological survival and social success and requires cognitive control, which is mediated by dorsomedial prefrontal cortex (DMPFC) and dorsolateral prefrontal cortex (DLPFC). How these brain regions communicate during conflict processing (detection, resolution, and adaptation), however, is still unknown. The Stroop task provides a well-established paradigm to investigate the cognitive mechanisms mediating such response conflict. Here, we explore the oscillatory patterns within and between the DMPFC and DLPFC in human epilepsy patients with intracranial EEG electrodes during an auditory Stroop experiment. Data from the DLPFC were obtained from 12 patients. Thereof four patients had additional DMPFC electrodes available for interaction analyses. Our results show that an early θ (4-8 Hz) modulated enhancement of DLPFC γ-band (30-100 Hz) activity constituted a prerequisite for later successful conflict processing. Subsequent conflict detection was reflected in a DMPFC θ power increase that causally entrained DLPFC θ activity (DMPFC to DLPFC). Conflict resolution was thereafter completed by coupling of DLPFC γ power to DMPFC θ oscillations. Finally, conflict adaptation was related to increased postresponse DLPFC γ-band activity and to θ coupling in the reverse direction (DLPFC to DMPFC). These results draw a detailed picture on how two regions in the prefrontal cortex communicate to resolve cognitive conflicts. In conclusion, our data show that conflict detection, control, and adaptation are supported by a sequence of processes that use the interplay of θ and γ oscillations within and between DMPFC and DLPFC.

Do surface DC-shifts affect epileptic hippocampal EEG activity?

Despite considerable research on EEG-feedback of slow cortical potentials (SCPs) for seizure control in epilepsy, the underlying mechanisms and the direct effects on intracerebral pathological activity within the focal area remain unclear. Intrahippocampal EEG recordings from four patients with temporal lobe epilepsy and implanted electrodes were analyzed with regard to spike activity and power in 10 frequency bands (0.5-148Hz) during SCP feedback based on surface recordings (position Cz). Trials with positive, negative and indifferent SCPs were contrasted. Three of the four patients showed changes in spike activity during SCPs, but these were inconsistent between patients, and resulted in increased and decreased activity in both positive and negative SCPs. Spectral analysis revealed that in all patients, positive surface shifts showed a bi-hemispheric higher power in the high-frequency activity above 40Hz. Two patients showed a higher power also during negative shifts, both in high-frequency activity and one in most other frequency bands. Feedback-related power effects did not differ between focal and non-focal side. The inconsistent change in spiking activity and the lack of decrease of power in pathology associated frequency bands during SCPs show that these SCPs do not decrease pathological activity within the epileptic focus. A possible relation of higher power in high-frequency activity during positive SCPs to cognitive processes, such as memory functions, is discussed.

From alpha to gamma: electrophysiological correlates of meditation-related states of consciousness.

Meditation practice is difficult to access because of its countless forms of appearances originating from the complexity of cultures it has to serve. This makes a suitable categorization for scientific use almost impossible. However, empirical data suggest that different forms of meditation show similar steps of development in terms of their neurophysiological correlates. Some electrophysiological alterations can be observed on the beginner/student level, which are closely related to non-meditative processes. Others seem to correspond to an advanced/expert level, and seem to be unique for meditation-related states of consciousness. Meditation is one possibility to specialize brain/mind functions using the brain's immanent neural plasticity. This plasticity is probably recruited by certain EEG patterns observed during or as a result of meditation, for instance, synchronized gamma oscillations. While meditation formerly has been understood to comprise mainly passive relaxation states, recent EEG findings suggest that meditation is associated with active states which involve cognitive restructuring and learning.

Activation of the caudal anterior cingulate cortex due to task-related interference in an auditory Stroop paradigm.

Successful information processing requires the focusing of attention on a certain stimulus property and the simultaneous suppression of irrelevant information. The Stroop task is a useful paradigm to study such attentional top-down control in the presence of interference. Here, we investigated the neural correlates of an auditory Stroop task using fMRI. Subjects focused either on tone pitch (relatively high or low; phonetic task) or on the meaning of a spoken word (high/low/good; semantic task), while ignoring the other stimulus feature. We differentiated between task-related (phonetic incongruent vs. semantic incongruent) and sensory-level interference (phonetic incongruent vs. phonetic congruent). Task-related interference activated similar regions as in visual Stroop tasks, including the anterior cingulate cortex (ACC) and the presupplementary motor-area (pre-SMA). More specifically, we observed that the very caudal/posterior part of the ACC was activated and not the dorsal/anterior region. Because identical stimuli but different task demands are compared in this contrast, it reflects conflict at a relatively high processing level. A more conventional contrast between incongruent and congruent phonetic trials was associated with a different cluster in the pre-SMA/ACC which was observed in a large number of previous studies. Finally, functional connectivity analysis revealed that activity within the regions activated in the phonetic incongruent vs. semantic incongruent contrast was more strongly interrelated during semantically vs. phonetically incongruent trials. Taken together, we found (besides activation of regions well-known from visual Stroop tasks) activation of the very caudal and posterior part of the ACC due to task-related interference in an auditory Stroop task.

Human neocortical and hippocampal near-DC shifts are interconnected.

Hippocampal DC shifts have been observed under various physiological and pathological conditions. Here, we studied the interconnection of slow shifts (0.01 Hz high-pass) in surface EEG and hippocampal shifts as emerging in an event-related EEG biofeedback paradigm. Hippocampal EEG activity was monitored by depth electrodes implanted in four epilepsy patients for presurgical evaluation. Trials were sorted according to the near-DC shifts occurring at the surface position Cz, which was the feedback electrode, into positive, indistinct (i.e., small or biphasic) and negative shifts. We found significant hippocampal near-DC shifts being positively or negatively correlated to the shifts in surface EEG in all four patients. The amplitudes of the hippocampal near-DC shifts were several times larger than the surface shifts. The polarity of the shifts appears to depend on the location of the electrode contacts with respect to the hippocampal subfields. The finding that neocortical and hippocampal near-DC shifts are interconnected may open new perspectives for the prediction and control of mediotemporal lobe seizures.