Y. Pavlov, Germany
University of Tuebingen Institute of Medical PsychologyPresenter of 4 Presentations
EPP0006 - The effects of sleep and wakefulness on human fear conditioning
ABSTRACT
Introduction
Studies on fear conditioning have made important contributions to the understanding of affective learning mechanisms as well as its applications (e.g., anxiety disorders, post-traumatic stress disorder). However, central mechanisms of sleep related consolidation of fear memory in humans have been almost neglected by previous studies.
Objectives
In the current study we aimed to test effects of sleep and a period wakefulness on fear conditioned responses.
Methods
In our experiment in a group 18 healthy volunteers event-related brain potentials (ERP), heart rate variability (HRV) and behavioral responses were recorded during a fear conditioning procedure presented twice, before daytime sleep (2h) or control intervention (a period of wakefulness) and after. The conditioning procedure involved pairing of a neutral tone (CS+) with a highly unpleasant sound (UCS+).
Results
Differential conditioning manifested itself in the contingent negative variance (CNV)-like slow ERP component. Both period of sleep and wakefulness resulted in an increased amplitude of the CNV to CS+. But we did not find an interaction effect of Time (Pre-Post) by Intervention (Sleep-Wake), suggesting that sleep did not affect the conditioned response differently as compared to a period of wakefulness. An apparent increase in HRV after a period of wakefulness did not affect fear conditioned responses (CNV and valence ratings).
Conclusions
To summarize, the data indicate that fear memories are consolidated with the course of time with no beneficial effect of sleep; relearning of fear causes stronger differential responses as measured by slow wave amplitude but not behavior; increase of HRV does not affect fear learning.
EPP0024 - Event-related potentials in a human serial conditioning paradigm
ABSTRACT
Introduction
In a serial compound conditioning paradigm, a sequence of several conditioned stimuli (CS) is predictive to an unconditioned stimulus (US) (e.g., CSA->CSB->US). Animal research showed that, when the US is aversive, CSA elicits the strongest conditioned response, while CSB appears redundant. These effects of primacy and proximity have never been investigated in humans.
Objectives
To study the effects of temporal proximity of imminent threat and safety in serial compound conditioning.
Methods
Twenty-two participants were presented with sequences [CSA->CSB->CSC->CSD]. In 55 trials all four CS were identical vowels (e.g, [oh]), and no US was presented. In the other 55 trials, the CSA was different (CSA+, e.g., [uh]), and the CSD was followed by an electrical shock (US) 2.5 times higher than the individual pain threshold.
Results
No ERP component distinguished between CS- and CS+ for the first three stimuli in the sequence (i.e., CSA, CSB, CSC). The last CS (CSD) elicited a strong fronto-central CNV only when it was followed by US. Moreover, already after the CSA- (which signalized that no shock would be presented on that trial) the power of alpha oscillations over the somatosensory cortex significantly increased, particularly on the side contralateral to the hand that was electrically stimulated on US trials. The alpha increment lasted up to the onset of the US.
Conclusions
The data indicate two possible mechanisms of adjustment to predictable threat, one of which relies on safety signals (manifested in alpha increment), and the other is related to flight response (manifested in the CNV immediately preceding the shock).
EPP1064 - Neural underpinnings of contingency awareness in human fear conditioning
ABSTRACT
Introduction
The recognition of the conditioned-unconditioned stimulus (CS-US) association in classical conditioning is referred to as contingency awareness. The neural underpinnings of contingency awareness in human fear conditioning are poorly understood.
Objectives
We aimed to explore the EEG correlates of contingency awareness.
Methods
Here, we recorded electroencephalography (EEG) from a sample of 20 participants in a semantic conditioning experiment. In the acquisition phase the participants were presented with sequences of words from two semantic categories paired with tactile stimulation followed by presentation of a neutral sound (US-) ((e.g., animals -> left hand vibration -> US-, clothes -> right hand vibration -> US-). In the test phase the association violated in 50% of trials which followed by a presentation of a loud noise (US+). The participants were only instructed to listen carefully. On the basis of self-reported contingency awareness, twenty participants were divided in aware (N=12) and unaware (N=8) group.
Results
The aware group expressed a non-lateralized effect of alpha-beta (12-23 Hz) suppression along with a more negative CNV at central channels preceding presentation of the vibration (main effect of Group). Also, CNV was more negative in expectation of US+ comparing with expectation of US- in the aware group but not in the unaware group.
Conclusions
The results indicate that contingency awareness is accompanied by neural patterns reflecting expectation as can be seen in the suppression of somatosensory alpha-beta activity before expected presentation of the vibration as well as in CNV in expectation of an aversive event.
EPP1073 - Working memory after and during 6 Hz transcranial alternating current stimulation
ABSTRACT
Introduction
Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique allowing to induce changes in oscillatory activity. Theta activity has been reported to play a major role in maintenance of information in working memory (WM).
Objectives
The current study had the initial goal to check the effect of theta tACS on accuracy and resting state EEG in a set of match-to-sample WM tasks.
Methods
In the first experiment, we tested 31 participants in the WM task after 20-min tACS applied at Fpz and CPz at 6 Hz, 1 mA. ). In the second experiment, we compared the after-effects and online effects of the stimulation in a sample of 25 individuals. Five similar 25-min blocks filled with the same working memory task were distributed over 3 days. We assessed the same group of participants in all three sessions. On the Training day, the participants performed one block without stimulation. On the Sham-Verum day (SV), the first block with Sham stimulation followed by the second block with Verum stimulation. On the Verum-Sham day (VS), the blocks order reversed.
Results
After-effects of the stimulation did not produce any significant changes either in behavior (accuracy in the task) or resting-state EEG (theta frequency band spectral power in the first experiment. In the second experiment, 6 Hz tACS delivered before the WM task was not able to produce any observable changes in working memory performance. The same hold true for online stimulation.
Conclusions
Theta frequency tACS applied to Fpz-CPz electrodes is not an efficient method to improve WM.