Ariane Keitel

Endocrine and psychological stress responses in a simulated emergency situation

BACKGROUND Several studies have assessed the effects of training using patient simulation systems on medical skills. However, endocrine and psychological stress responses in a patient simulation situation and the relationship between stress reactivity and medical performance have been studied rarely, so far. METHODS Medical students (18 males and 16 females) who had completed at least two months anaesthesiology training participated in the study. In a counterbalanced cross-over design they were subjected to three conditions: rest, laboratory stress (LS; public speaking), and simulated emergency situation (SIM; myocardial ischemia and ventricular fibrillation). Salivary cortisol and psychological responses (visual analogue scales, VAS) were assessed every 15 min from 15 min prior to until 60 min after intervention. Differences between stress and rest conditions were analysed. Medical performance was assessed according to the European Resuscitation Councils Guidelines for Resuscitation. RESULTS As compared to rest, cortisol increased significantly in both stress conditions with different time courses in LS and SIM. Psychological responses in SIM exceeded those in LS. Cortisol increase in LS (r(s)=.486; p=.019) but not in SIM (r(s)=.106; p=.631) correlated significantly with medical performance. DISCUSSION A simulated emergency situation is a profound stressor. The positive relationship between endocrine stress responsiveness in a standard laboratory situation and medical performance in a simulated emergency situation indicates that high stress responsiveness might be a predictor of good performance. At the same time the high stress response might counteract educational efforts associated with training using high-fidelity patient simulation.

Motor and cognitive placebo-/nocebo-responses in Parkinson's disease patients with deep brain stimulation.

Expectation contributes to placebo and nocebo responses in Parkinsons disease (PD). Subthalamic nucleus (STN) deep brain stimulation (DBS) improves proximal more than distal movements whereas it impairs executive cognitive function such as verbal fluency (VF). We investigated how expectation modulates the pattern of motor improvement in STN-DBS and its interaction with VF. In a within-subject-design, expectation of 24 hypokinetic-rigid PD patients regarding the impact of STN-DBS on motor symptoms was manipulated by verbal suggestions (positive [placebo], negative [nocebo], neutral [control]). Patients participated with (MedON) and without (MedOFF) antiparkinsonian medication. Motor function was assessed by Unified Parkinsons Disease Rating Scale and quantitative kinematic analysis of proximal alternating hand and distal finger tapping. VF was quantified by lexical and semantic tests. In MedOFF, expectation significantly affected proximal but not distal movements resulting in better performance in the placebo than in the nocebo condition. Placebo responders with improvement of ≥25% were characterized by a trend for impaired lexical VF. These results indicate that positive motor expectations exert both motor placebo and cognitive nocebo responses by further enhancing the STN-DBS-effect on proximal movements and by impairing VF. The placebo response on motor performance resembles the clinically known STN-DBS-effect with stronger improvement in proximal than distal movements. The nocebo response on VF is likely due to implicit learning mechanisms associated with an expectation-induced placebo response on motor performance.

The Posterior Parietal Cortex Subserves Precise Motor Timing in Professional Drummers

The synchronization task is a well-established paradigm for the investigation of motor timing with respect to an external pacing signal. It requires subjects to synchronize their finger taps in synchrony with a regular metronome. A specific significance of the posterior parietal cortex (PPC) for superior synchronization in professional drummers has been suggested. In non-musicians, modulation of the excitability of the left PPC by means of transcranial direct current stimulation (tDCS) modulates synchronization performance of the right hand. In order to determine the significance of the left PPC for superior synchronization in drummers, we here investigate the effects of cathodal and anodal tDCS in 20 professional drummers on auditory-motor synchronization of the right hand. A continuation and a reaction time task served as control conditions. Moreover, the interaction between baseline performance and tDCS polarity was estimated in precise as compared to less precise synchronizers according to median split. Previously published data from 16 non-musicians were re-analyzed accordingly in order to highlight possible differences of tDCS effects in drummers and non-musicians. TDCS was applied for 10 min with an intensity of 0.25 mA over the left PPC. Behavioral measures were determined prior to and immediately after tDCS. In drummers the overall analysis of synchronization performance revealed significantly larger tap-to-tone asynchronies following anodal tDCS with the tap preceding the tone replicating findings in non-musicians. No significant effects were found on control tasks. The analysis for participants with large as compared to small baseline asynchronies revealed that only in drummers with small asynchronies tDCS interfered with synchronization performance. The re-analysis of the data from non-musicians indicated the reversed pattern. The data support the hypothesis that the PPC is involved in auditory-motor synchronization and extend previous findings by showing that its functional significance varies with musical expertise.

Cathodal transcranial direct current stimulation (tDCS) applied to the left premotor cortex (PMC) stabilizes a newly learned motor sequence

HighlightsLeft PMC tDCS during motor sequence learning does not affect reaction times.Left PMC tDCS prior to motor sequence learning non‐specifically facilitates reaction times.Cathodal PMC tDCS prior to motor sequence learning yields reduced interference.The PMC might be related to stabilization but not acquisition of a motor sequence. ABSTRACT While the primary motor cortex (M1) is involved in the acquisition the premotor cortex (PMC) has been related to over‐night consolidation of a newly learned motor skill. The present study aims at investigating the possible contribution of the left PMC for the stabilization of a motor sequence immediately after acquisition as determined by susceptibility to interference. Thirty six healthy volunteers received anodal, cathodal and sham transcranial direct current stimulation (tDCS) to the left PMC either immediately prior to or during training on a serial reaction time task (SRTT) with the right hand. TDCS was applied for 10 min, respectively. Reaction times were measured prior to training (t1), at the end of training (t2), and after presentation of an interfering random pattern (t3). Beyond interference from learning, the random pattern served as control condition in order to estimate general effects of tDCS on reaction times. TDCS applied during SRTT training did not result in any significant effects neither on acquisition nor on susceptibility to interference. In contrast to this, tDCS prior to SRTT training yielded an unspecific facilitation of reaction times at t2 independent of tDCS polarity. At t3, reduced susceptibility to interference was found following cathodal stimulation. The results suggest the involvement of the PMC in early consolidation and reveal a piece of evidence for the hypothesis that behavioral tDCS effects vary with the activation state of the stimulated area.

Implicit Motor Sequence Learning and Working Memory Performance Changes Across the Adult Life Span

Although implicit motor sequence learning is rather well understood in young adults, effects of aging on this kind of learning are controversial. There is first evidence that working memory (WM) might play a role in implicit motor sequence learning in young adults as well as in adults above the age of 65. However, the knowledge about the development of these processes across the adult life span is rather limited. As the average age of our population continues to rise, a better understanding of age-related changes in motor sequence learning and potentially mediating cognitive processes takes on increasing significance. Therefore, we investigated aging effects on implicit motor sequence learning and WM. Sixty adults (18–71 years) completed verbal and visuospatial n-back tasks and were trained on a serial reaction time task (SRTT). Randomly varying trials served as control condition. To further assess consolidation indicated by off-line improvement and reduced susceptibility to interference, reaction times (RTs) were determined 1 h after initial learning. Young and older but not middle-aged adults showed motor sequence learning. Nine out of 20 older adults (compared to one young/one middle-aged) exhibited some evidence of sequence awareness. After 1 h, young and middle-aged adults showed off-line improvement. However, RT facilitation was not specific to sequence trials. Importantly, susceptibility to interference was reduced in young and older adults indicating the occurrence of consolidation. Although WM performance declined in older participants when load was high, it was not significantly related to sequence learning. The data reveal a decline in motor sequence learning in middle-aged but not in older adults. The use of explicit learning strategies in older adults might account for the latter result.

The Significance of the Right Dorsolateral Prefrontal Cortex for Pitch Memory in Non-musicians Depends on Baseline Pitch Memory Abilities

Pitch memory is a resource which is shared by music and language. Neuroimaging studies have shown that the right dorsolateral prefrontal cortex (DLPFC) is activated during pitch memory processes. The present study investigated the causal significance of this brain area for pitch memory in non-musicians by applying cathodal and sham transcranial direct current stimulation (tDCS) over the right DLPFC and examining the impact on offline pitch and visual memory span performances. On the overall sample (N = 22) no significant modulation effect of cathodal stimulation on the pitch span task was found. However, when dividing the sample by means of a median split of pre-test pitch memory abilities into a high and low performing group, a selective effect of significantly impaired pitch memory after cathodal tDCS in good performers was revealed. The visual control task was not affected by the stimulation in either group. The results support previous neuroimaging studies that the right DLPFC is involved in pitch memory processes in non-musicians and highlights the importance of baseline pitch memory abilities for the modulatory effect of tDCS.

EP 129. The effect of tDCS over M1 prior to and during implicit motor sequence learning

Motor learning is an essential skill allowing the acquisition of new movement patterns. Transcranial direct current stimulation (tDCS) has been shown to modulate neuronal excitability along with behavioural performance in a polarity-dependent manner. Besides polarity, the effects of tDCS on motor learning also vary with the timing of stimulation. In order to gain a better understanding regarding the optimal timing of tDCS application to modulate implicit motor sequence learning, motor-cortical tDCS was applied prior to and during training on a serial reaction time task (SRTT). The SRTT employs a fixed sequential pattern of button presses allowing the assessment of implicit motor sequence learning. A random pattern served as control condition. 36 healthy subjects were assigned to one of two experiments: tDCS was applied prior to (experiment 1) or during (experiment 2) SRTT training. Anodal vs. cathodal vs. sham tDCS was applied to the left primary motor cortex (M1) for ten minutes in a counterbalanced order. Reaction times of the right hand were measured at Baseline and after SRTT training (End of Acquisition (EoA)). Anodal tDCS prior to SRTT training yielded a beneficial effect on the acquisition of the motor sequence, i.e. reaction times decreased significantly from Baseline to EoA in the sequential pattern. Moreover, at EoA, reaction times were significantly faster following anodal as compared to cathodal tDCS. Reaction times of the random pattern were not differentially modulated by stimulation polarity indicating a sequence-specific effect. In contrast, tDCS applied during SRTT training did not differentially modulate the acquisition of the motor sequence. These results indicate that the timing of tDCS is a crucial parameter yielding distinct effects on implicit motor sequence learning. Anodal tDCS prior to SRTT training resulted in a facilitation emphasising a beneficial effect of increased left M1 excitability for the subsequent acquisition of a new motor sequence. In contrast, modulation of motor-cortical excitability by tDCS during SRTT training yielded no differential effects. This finding implies that tDCS effects may vary with the activation level during stimulation (rest vs. movement).

Anodal Transcranial Direct Current Stimulation (tDCS) Over the Right Primary Motor Cortex (M1) Impairs Implicit Motor Sequence Learning of the Ipsilateral Hand

Motor sequence learning is associated with the activation of bilateral primary motor cortices (M1). While previous data support the hypothesis that the contralateral M1 is causally involved in the acquisition as well as early consolidation of a motor sequence, the functional significance of the ipsilateral M1 has yet to be solved. Transcranial direct current stimulation (tDCS) allows the non-invasive modulation of cortical excitability. Anodal tDCS applied to the left M1 has been shown to facilitate implicit motor sequence learning of the right hand most likely due to increased excitability. The present study aims at characterizing the functional contribution of the ipsilateral (right) M1 on implicit motor sequence learning of the right hand. To this end, 24 healthy, right-handed subjects received anodal and sham tDCS to the right M1 in a counterbalanced order. Stimulation started 8 min prior to training on a variant of the serial reaction time task (SRTT) with the right hand and persists over the entire training period. The SRTT comprised a fixed eight-digit sequence. A random pattern served as control condition. Reaction times were assessed before and at the end of the acquisition (EoA) immediately after training on the SRTT. The analysis revealed significantly faster reaction times of both hands independent of tDCS condition in sequential trials. However, the gain of reaction times was significantly smaller following anodal as compared to sham tDCS. The data suggest that anodal tDCS applied to the right M1 impairs implicit motor sequence learning of both hands. The underlying mechanism likely involves alterations of the interaction between bilateral M1.

Transcranial direct current stimulation (tDCS) applied to the left dorsolateral premotor cortex (dPMC) interferes with rhythm reproduction

Movement timing in the sub-second range engages a brain network comprising cortical and sub-cortical areas. The present study aims at investigating the functional significance of the left dorsolateral premotor cortex (dPMC) for precise movement timing as determined by sensorimotor synchronization and rhythm reproduction. To this end, 18 healthy volunteers performed an auditorily paced synchronization-continuation task with the right hand. A simple reaction time task served as control condition. Transcranial direct current stimulation (tDCS) was applied over the left dPMC in order to modulate cortical excitability either with anodal or cathodal polarity or as sham stimulation. TDCS was applied for 10 minutes, respectively on separate days. For the continuation task the analysis revealed significantly smaller inter-tap intervals (ITIs) following cathodal tDCS suggesting movement hastening as well as a trend towards larger ITIs following anodal stimulation suggesting movement slowing. No significant effect was found following sham stimulation. Neither for synchronization nor for reaction time tasks significant polarity-specific effects emerged. The data suggest the causal involvement of the dPMC in temporally precisereproduction of isochronous rhythms rather than sensorimotor synchronization. The present findings support the hypothesis that different cortical brain areas within the motor-control-network distinctively contribute to movement timing in the sub-second range.

EP 128. Motor learning: TDCS effects vary with baseline performance

Transcranial direct current stimulation (tDCS) allows the non-invasive modulation of cortical excitability. Anodal tDCS is associated with an increase of cortical excitability, while cathodal tDCS yields its decrease. Beyond altered excitability, tDCS to the primary motor cortex (M1) has been proven to modulate motor performance, but effects considerably vary across participants. To further elucidate the indicative role of baseline performance on the impact of tDCS, we subdivided 72 participants after baseline reaction time recordings into fast and slow performers by median split. Subsequently, participants implicitly learned a motor sequence with the right hand using the serial reaction time task. M1 is assumed to contribute to motor sequence acquisition and early motor memory consolidation, while the premotor cortex (PMC) may be relevant for later phases of consolidation. In half of the participants, tDCS was applied to the left M1 and in the other half to the left PMC. Since tDCS effects also vary with respect to timing of stimulation, tDCS was applied either prior to or during motor sequence learning. Anodal vs. cathodal vs. sham tDCS was applied in three separate sessions. When tDCS was applied prior to learning, anodal M1 tDCS facilitated subsequent sequence acquisition. Most interestingly, this effect became evident in participants with slow baseline reaction times only. When tDCS was applied during learning, anodal M1 tDCS yielded an unspecific facilitation of reaction times – again in participants with slow baseline performance only. Cathodal and sham tDCS as well as PMC tDCS had no such effect. Fast performers did not benefit from tDCS possibly due to a ceiling effect. Beyond underpinning the relevance of M1 for initial motor sequence acquisition, the present results complement evidence that behavioural tDCS effects may strongly depend on the behavioural status quo at time of stimulation.