Peter Trautner

Social Comparison Affects Reward-Related Brain Activity in the Human Ventral Striatum

Whether social comparison affects individual well-being is of central importance for understanding behavior in any social environment. Traditional economic theories focus on the role of absolute rewards, whereas behavioral evidence suggests that social comparisons influence well-being and decisions. We investigated the impact of social comparisons on reward-related brain activity using functional magnetic resonance imaging (fMRI). While being scanned in two adjacent MRI scanners, pairs of subjects had to simultaneously perform a simple estimation task that entailed monetary rewards for correct answers. We show that a variation in the comparison subjects payment affects blood oxygenation level–dependent responses in the ventral striatum. Our results provide neurophysiological evidence for the importance of social comparison on reward processing in the human brain.

Neural Bases of Cognitive ERPs: More than Phase Reset

Up to now, two conflicting theories have tried to explain the genesis of averaged event-related potentials (ERPs): Whereas one hypothesis claims that ERPs originate from an event-related activation of neural assemblies distinct from background dynamics, the other hypothesis states that ERPs are produced by phase resetting of ongoing oscillatory activity. So far, this question has only been addressed for early ERP components. Late ERP components, however, are generally thought to represent superimposed activities of several anatomically distinct brain areas. Thus, the question of which mechanism underlies the genesis of late ERP components cannot be easily answered based on scalp recordings. In contrast, two well-investigated late ERP components recorded invasively from within the human medial temporal lobe (MTL) in epilepsy patients, the so-called MTL-P300 and the anterior MTL-N400 (AMTL-N400), are based on single source activity. Hence, we investigated whether the MTL-P300 and the AMTL-N400 are based on an event-related activity increase, a phase reset of ongoing oscillatory activity or both. ERPs were recorded from the hippocampus and rhinal cortex in subjects performing a visual oddball paradigm and a visual word recognition paradigm. With wavelet techniques, stimulus-related phase-locking and power changes were analyzed in a frequency range covering 2 to 48 Hz. We found that the MTLP300 is accompanied by both phase reset and power increase and that both effects overlap partly in time. In contrast, the AMTL-N400 is initially associated with phase locking without power increase and only later during the course of the AMTL-N400 we observed an additional power increase. In conclusion, both aspects, event-related activation of neural assemblies and phase resetting of ongoing activity seem to be involved in the generation of late ERP components as recorded in cognitive tasks. Therefore, separate analysis of event-related power and phase-locking changes might reveal specific insights into the mechanisms underlying different cognitive functions.

Neural evidence for Reference-dependence in real-market-transactions.

Human decision making has become one of the major research-foci in economics, marketing and in neuroscience. This study integrates perspectives from these disciplines by examining neurophysiological correlates to Reference-dependence of utility evaluations in real market contexts both before and after choice. First, by comparing buying and selling decisions, we observe an activation of the amygdala only in the latter. We interpret this as loss aversion with respect to prior possessions. This finding contributes to the settling of an ongoing fundamental dispute in economic theory by indicating the absence of loss aversion for money in routine transactions. Second, ex post satisfaction statements are accompanied by an activation of the reward processing orbitofrontal cortex, if the evaluation context is framed by a high external reference price instead of a lower internal reference price. This indicates a nonrational Reference-dependence--despite the neoclassical view of a rational Homo Economicus--of satisfaction measures and challenges a central marketing variable.

Sensory gating in the human hippocampal and rhinal regions

OBJECTIVE The objective of this work was to ascertain if sensory gating can be demonstrated within the human medial temporal lobe. METHODS Eight patients with intractable epilepsy with depth electrodes implanted in the medial temporal lobe for pre-surgery evaluation underwent evoked response recording to auditory paired-stimuli (S1-S2). Each of the eight subjects had a diagnosis of left medial temporal lobe epilepsy (MTLE). RESULTS Data from the non-focal right hippocampi revealed a large negative response on S1 (starting at about 190 ms and lasting for approximately 300 ms from stimulus onset). Rhinal region recordings revealed a positive response (starting at about 240 ms with a rapid incline, followed by a long-lasting decline). A significant attenuation of both responses to S2 stimuli was observed. CONCLUSIONS Data are suggestive of an involvement of the human medial temporal lobe in the processing of simple auditory information which occurs in a time frame later than the neocortical auditory evoked components. The exact role of these anatomical structures in the sensory gating process remains to be defined. SIGNIFICANCE This study provides the first evidence of an activation of the rhinal cortex after simple auditory stimulation and provides new evidence that the activation of the medial temporal lobe structures occurs at a later stage than that of the neocortex.

Short-term habituation of the intracranially recorded auditory evoked potentials P50 and N100

At an interstimulus interval (ISI) of 500-ms stimulus repetition leads to a strong decrease in cortical response. The functional foundation of this response suppression (or sensory gating) is yet not fully understood. Experiments on short-term habituation using the same stimulus material as sensory gating experiments and same ISI might help to elucidate the mechanisms behind the P50 suppression. Event-related potentials were recorded intracranially in epileptic patients undergoing presurgical evaluation with subdural and depth electrodes. Stimulus material consisted of trains of six clicks, with the last stimulus deviating in pitch and duration. P50 and N100 were calculated for each stimulus in the train separately and compared by analysis of variance (ANOVA). A highly significant amplitude reduction was found from the 1st to 2nd stimulus for both P50 and N100. From the 2nd to 5th stimulus no further amplitude decrease was observable. The deviating 6th stimulus led to a response recovery of both components, but the P50 elicited by the 6th stimulus was still smaller than the P50 of the 1st stimulus. Current results indicate that the P50 suppression as investigated in sensory gating experiments seems to be completed after the 2nd stimulus.

Widespread affections of large fiber tracts in postoperative temporal lobe epilepsy.

Temporal lobe epilepsy with hippocampus sclerosis (HS) is the most frequent focal epilepsy and often refractory to anticonvulsant therapy. Secondary structural damage has been reported in several studies of temporal lobe epilepsy and unilateral hippocampal sclerosis. Applying diffusion tensor imaging (DTI) we investigated alterations in white matter following temporal lobe surgery in patients with medial temporal lobe epilepsy. We examined 40 patients who underwent surgery at our hospital for HS between 1996 and 2006 with diffusion tensor imaging (DTI). Images were obtained at a 3 T MRI scanner employing 60 gradient directions. Tract-based spatial statistics (TBSS), a novel voxel-based approach, was applied to analyze the data. Both patients with left- as well as right-sided surgery exhibited widespread degradation of fractional anisotropy (FA) in main fiber tracts not limited to the respective temporal lobe such as the uncinate fasciculus, the fronto-occipital fasciculus, the superior longitudinal fasciculus, the corpus callosum and the corticospinal tract on the respective hemisphere. Patients with left-hemispheric surgery showed more widespread affections ipsilaterally and also FA decrease in the contralateral inferior longitudinal fasciculus. DTI demonstrates widespread clusters of abnormal diffusivity and anisotropy in prominent white matter tracts linking mesial temporal lobe structures with other brain areas. Alterations in the ipsilateral mesial temporal lobe can be attributed to be a result of surgery, whereas extratemporal FA decrease is more likely the result of the underlying seizure disorder.

Sensory gating of auditory evoked and induced gamma band activity in intracranial recordings

Oscillatory activity in the gamma band range (30-50 Hz) and its functional relation to auditory evoked potentials (AEPs) is yet poorly understood. In the current study, we capitalized on the advantage of intracranial recordings and studied gamma band activity (GBA) in an auditory sensory gating experiment. Recordings were obtained from the lateral surface of the temporal lobe in 34 epileptic patients undergoing presurgical evaluation. Two kinds of activity were differentiated: evoked (phase locked) and induced (not phase locked) GBA. In 18 patients, an intracranial P50 was observed. At electrodes with maximal P50, evoked GBA occurred with a similar peak latency as the P50. However, the intensities of P50 and evoked GBA were only modestly correlated, suggesting that the intracranial P50 does not represent a subset of evoked GBA. The peak frequency of the intracranial evoked GBA was on average relatively low (approximately 25 Hz) and is, therefore, probably not equivalent to extracranially recorded GBA which has normally a peak frequency of approximately 40 Hz. Induced GBA was detected in 10 subjects, nearly exclusively in the region of the superior temporal lobe. The induced GBA was increased after stimulation for several hundred milliseconds and encompassed frequencies up to 200 Hz. Single-trial analysis revealed that induced GBA occurred in relatively short bursts (mostly <<100 ms), indicating that the duration of the induced GBA in the averages originates from summation effects. Both types of gamma band activity showed a clear attenuation with stimulus repetition.

Retest reliability of reward-related BOLD signals.

Reward processing is a central component of learning and decision making. Functional magnetic resonance imaging (fMRI) has contributed essentially to our understanding of reward processing in humans. The strength of reward-related brain responses might prove as a valuable marker for, or correlate of, individual preferences or personality traits. An essential prerequisite for this is a sufficient reliability of individual measures of reward-related brain signals. We therefore determined test-retest reliabilities of BOLD responses to reward prediction, reward receipt and reward prediction errors in the ventral striatum and the orbitofrontal cortex in 25 subjects undergoing three different simple reward paradigms (retest interval 7-13 days). Although on a group level the paradigms consistently led to significant activations of the relevant brain areas in two sessions, across-subject retest reliabilities were only poor to fair (with intraclass correlation coefficients (ICCs) of -0.15 to 0.44). ICCs for motor activations were considerably higher (ICCs 0.32 to 0.73). Our results reveal the methodological difficulties behind across-subject correlations in fMRI research on reward processing. These results demonstrate the need for studies that address methods to optimize the retest reliability of fMRI.

Cerebellar contributions to episodic memory encoding as revealed by fMRI

Event-related functional Magnetic Resonance Imaging (fMRI) allows for the comparison of hemodynamic responses evoked by items that are remembered in a subsequent memory task vs. items that are forgotten. In this way, brain regions that assumingly contribute to successful memory encoding have been identified, including the left inferior prefrontal cortex (LIPC) and the medial temporal lobe. Although a cerebellar involvement in verbal working memory is well-established, a contribution of the cerebellum to episodic long-term encoding has only sporadically been described, and mechanisms underlying cerebellar memory effects are unclear. We conducted a typical incidental verbal memory fMRI experiment with three different encoding tasks varying the depth of semantic processing. Slice positioning allowed for the coverage of the entire cerebellum. We observed a significant subsequent memory effect within the superior and posterior right cerebellar hemisphere that was task independent. Additionally, we found a different area within the superior right cerebellum displaying a memory effect specifically for semantically processed words and a bilateral cerebellar activation specifically associated with encoding success only for a non-semantic task. Our results suggest that besides its known role in verbal working memory, the cerebellum contributes to episodic long-term encoding and should therefore be considered in future fMRI studies dealing with episodic memory.

Hippocampal event-related potentials to tone duration deviance in a passive oddball paradigm in humans.

The mismatch negativity (MMN), a component of event-related potentials (ERPs), is assumed to reflect a preattentive auditory discrimination process. Although an involvement of hippocampal structures in deviance detection was shown in animal experiments, invasive recordings in humans have not been able to provide such an evidence so far. In the current study, ERPs were recorded from intrahippocampal and scalp electrodes in 16 epilepsy patients. Stimulation consisted of trains of six tones, with one tone deviating in duration (100 vs. 50 ms). In the rhinal cortex, ERPs elicited by deviants were larger in amplitude than those of standards (around 200 ms). The rhinal activation was succeeded by a long-lasting hippocampal ERP component (around 350 ms). However, in contrast to the rhinal activation, hippocampal activation was also elicited by the 1st stimuli of the train and might, therefore, be related more to salience detection than to deviance detection. The current study provides evidence that the MMN is part of a multistage comparison process and that the rhinal cortex is part of its underlying cortical network.