ObjectiveThe time interval between transcranial magnetic stimulation pulses affects evoked muscle responses when the targeted muscle is resting. This necessitates using sufficiently long inter-pulse intervals. However, there is some evidence that the IPI has no effect on the responses evoked in active muscles. Thus, we tested whether voluntary contraction could remove the effect of the IPI on TMS motor evoked potentials.MethodsIn our study, we delivered sets of 30 TMS pulses with three different IPIs to the left primary motor (...) cortex. These measurements were performed with the resting and active right hand first dorsal interosseous muscle in healthy participants. MEP amplitudes were recorded through electromyography.ResultsWe found that the IPI had no significant effect on the MEP amplitudes in the active muscle, whereas in the resting muscle, the IPI significantly affected the MEP amplitudes, decreasing the MEP amplitude of the 2 s IPI.ConclusionsThese results show that active muscle contraction removes the effect of the IPI on the MEP amplitude. Therefore, using active muscles in TMS motor mapping enables faster delivery of TMS pulses, reducing measurement time in novel TMS motor mapping studies. (shrink)

1 – Institute for Frontier Areas of Psychology and Mental Health, Wilhelmstr. 3a, 79098 Freiburg, Germany 2 – Parmenides Center, Via Mellini 26-28, 57031 Capoliveri, Italy 3 – Department of Ophtalmology, University of Freiburg, Killianstr. 5, 79106 Freiburg, Germany 4 – Institute of Physics, University of Freiburg, Hermann- Herder -Str. 3, 79104 Freiburg, GermanyThe “Necker-Zeno model”, a model for bistable perception inspired by the quantum Zeno effect, was previously used to relate three basic time scales of cognitive relevance to one (...) another in a quantitative manner. In this paper, the model predictions are compared with experimental results obtained under discontinuous presentation of an ambiguous stimulus. In addition to earlier results for long inter-stimulus intervals, we show that the reversal dynamics according to the Necker-Zeno model is also in agreement with new results for short inter-stimulus intervals. Moreover, we refine the model in such a way that it accounts for the distribution of “dwell times”. Finally, we indicate applications concerning the modification of cognitive time scales under conditions of psychopathological impairments and meditationinduced modes of awareness. ∗Address correspondence to this author at the Theory Division of the Institute for Frontier Areas of Psychology, Wilhelmstr. 3a, D–79098 Freiburg, Germany; E-mail: [email protected]. (shrink)

Participants of low and high hypnotic susceptibility were tested on a temporal order judgement task, both with and without hypnosis. Judgements were made of the order of presentation of light flashes appearing in first one hemi-field then the other. There were differences in the inter-stimulus intervals required accurately to report the order, depending upon which hemi-field led. This asymmetry was most marked in hypnotically susceptible participants and reversed when they were hypnotised. This implies not only that brain activity (...) changes in hypnosis, but also that there is a difference in brain function between people of low and high hypnotic susceptibility. The latter exhibited a faster-acting left hemisphere in the waking state, but faster right when hypnotised. (shrink)

Embodied theories of language postulate that language meaning is stored in modality-specific brain areas generally involved in perception and action in the real world. However, the temporal dynamics of the interaction between modality-specific information and lexical-semantic processing remain unclear. We investigated the relative timing at which two types of modality-specific information (action-based and visual-form information) contribute to lexical-semantic comprehension. To this end, we applied a behavioral priming paradigm in which prime and target words were related with respect to (1) action (...) features, (2) visual features, or (3) semantically associative information. Using a Go/No-Go lexical decision task, priming effects were measured across four different inter-stimulus intervals (ISI = 100, 250, 400, and 1000 ms) to determine the relative time course of the different features. Notably, action priming effects were found in ISIs of 100, 250, and 1000 ms whereas a visual priming effect was seen only in the ISI of 1000 ms. Importantly, our data suggest that features follow different time courses of activation during word recognition. In this regard, feature activation is dynamic, measurable in specific time windows but not in others. Thus the current study (1) demonstrates how multiple ISIs can be used within an experiment to help chart the time course of feature activation and (2) provides new evidence for embodied theories of language. (shrink)

After spinal cord injury (SCI), motoneuron death occurs at and around the level of injury which induces changes in function and organization throughout the nervous system, including cortical changes. Muscle affected by SCI may consist of both innervated (accessible to voluntary drive) and denervated (inaccessible to voluntary drive) muscle fibers. Voluntary activation measured with transcranial magnetic stimulation (VATMS) can quantify voluntary cortical/subcortical drive to muscle but is limited by technical challenges including suboptimal stimulation of target muscle relative to its antagonist. (...) The motor evoked potential (MEP) in the biceps compared to the triceps (i.e., MEP ratio) may be a key parameter in the measurement of biceps VATMS after SCI. We used paired pulse TMS, which can inhibit or facilitate MEPs, to determine whether the MEP ratio affects VATMS in individuals with tetraplegia. Ten individuals with tetraplegia following cervical SCI and ten non-impaired individuals completed single pulse and paired pulse VATMS protocols. Paired pulse stimulation was delivered at 1.5, 10, and 30 ms inter-stimulus intervals (ISI). In both the SCI and non-impaired groups, the main effect of the stimulation pulse (paired pulse compared to single pulse) on VATMS was not significant in the linear mixed-effects models. In both groups for the stimulation parameters we tested, the MEP ratio was not modulated across all effort levels and did not affect VATMS. Linearity of the voluntary moment and superimposed twitch moment relation was lower in SCI participants compared to non-impaired. Poor linearity in the SCI group limits interpretation of VATMS. Future work is needed to address methodological issues that limit clinical application of VATMS. (shrink)

Humans have a flexible and accurate ability to coordinate their movement in time with external rhythms. However, it remains unclear when and how, during their development, human children acquire the ability to adjust tempo and control the timing of their movement toward others. A previous study suggested that such self-regulation of coordination develops at around 18 and 30 months after birth. In this study, we investigated the performance of 24-month-old children and compared their data with those of 18- and 30-month-olds (...) provided in our previous study. In the joint-drumming task, each child was enticed to drum under four conditions [partner: mother or robot; speed: 400 or 600 ms inter-stimulus-interval ]. The most pivotal test condition was the 600 ms ISI speed condition. We found that from the age of 24 months, children try to slow down their drumming tempo toward the 600 ms ISI speed condition, regardless of the drumming partner. On the other hand, significant timing control toward the onset of the 600 ms ISI condition was observed from the age of 30 months. This implies that both motor and cognitive mechanisms are required for flexible tempo adjustment and accurate synchronization and that these develop gradually among 18-, 24-, and 30-month-olds. (shrink)

The fundamental relations that underlie cognitive comparisons—“same” and “different”—can be defined at multiple levels of abstraction, which vary in relational complexity. We compared response times to decide whether or not two sequentially‐presented patterns, each composed of two pairs of colored squares, were the same at three levels of abstraction: perceptual, relational, and system (higher order relations). For both 150 ms and 5 s inter‐stimulus intervals (ISIs), both with and without a masking stimulus, decision time increased with level (...) of abstraction. Sameness at lower complexity levels contributed to decisions based on the higher levels. The pattern of comparison times across levelswas not predictable solely from encoding times. The results indicated that relations at multiple levels of complexity can be abstracted and compared in working memory, with higher complexity levels requiring more processing time. We simulated the impact of relational complexity on response time using Learning and Inference with Schemas and Analogies (LISA), a computational model of relational comparisons based on dynamic binding of elements into roles in a relational working memory. (shrink)

The fundamental relations that underlie cognitive comparisons—“same” and “different”—can be defined at multiple levels of abstraction, which vary in relational complexity. We compared response times to decide whether or not two sequentially‐presented patterns, each composed of two pairs of colored squares, were the same at three levels of abstraction: perceptual, relational, and system (higher order relations). For both 150 ms and 5 s inter‐stimulus intervals (ISIs), both with and without a masking stimulus, decision time increased with level (...) of abstraction. Sameness at lower complexity levels contributed to decisions based on the higher levels. The pattern of comparison times across levelswas not predictable solely from encoding times. The results indicated that relations at multiple levels of complexity can be abstracted and compared in working memory, with higher complexity levels requiring more processing time. We simulated the impact of relational complexity on response time using Learning and Inference with Schemas and Analogies (LISA), a computational model of relational comparisons based on dynamic binding of elements into roles in a relational working memory. (shrink)

Short-term motor practice leads to plasticity in the primary motor cortex. The purpose of this study is to investigate the factors that determine the increase in corticospinal tract excitability after motor practice, with special focus on two factors; “the level of muscle activity” and “the presence/absence of a goal of keeping the activity level constant.” Fifteen healthy subjects performed four types of rapid thumb adduction in separate sessions. In the “comfortable task” and “forceful task”, the subjects adducted their thumb using (...) comfortable and strong forces. In the “comfortable with a goal task” and “forceful with a goal task”, subjects controlled the muscle activity at the same level as in the C and F, respectively, by adjusting the peak electromyographic amplitude within the target ranges. Paired associative stimulation, which combines peripheral nerve stimulation and transcranial magnetic stimulation, with an inter-stimulus interval of 25 ms was also done. Before and after the motor tasks and PAS25, TMS was applied to the M1. None of the four tasks showed any temporary changes in behavior, meaning no learning occurred. Motor-evoked potential amplitude increased only after the FG and it exhibited a positive correlation with the MEP increase after PAS25, suggesting that FG and PAS25 share at least similar plasticity mechanisms in the M1. Resting motor threshold decreased only after FG, suggesting that FG would also be associated with the membrane depolarization of M1 neurons. These results suggest task-dependent plasticity from the synergistic effect of forceful muscle activity and of setting a goal of keeping the activity level constant. (shrink)

The current contents of visual working memory can be disrupted by previously formed memories. This phenomenon is known as proactive interference, and it can be used to index the availability of old memories. However, there is uncertainty about the robustness and lifetime of proactive interference, which raises important questions about the role of temporal factors in forgetting. The present study assessed different factors that were expected to influence the persistence of proactive interference over an inter-trial interval in the (...) visual recent probes task. In three experiments, participants encoded arrays of targets and then determined whether a single probe matched one of those targets. On some trials, the probe matched an item from the previous trial, whereas on other trials the probe matched a more distant item. Prior studies have found that recent negative probes can increase errors and slow response times in comparison to non-recent negative probes, and this offered a behavioral measure of proactive interference. In Experiment 1, factors of array size and inter-trial interval were manipulated in the recent probes task. There was a reduction in proactive interference when a longer delay separated trials on one measure, but only when participants encoded two targets. When working memory capacity was strained by increasing the array size to four targets, proactive interference became stronger after the long delay. In Experiment 2, the inter-trial interval length was again manipulated, along with stimulus novelty. Proactive interference was modestly stronger when a smaller number of stimuli were used throughout the experiment, but proactive interference was minimally affected by the inter-trial interval. These findings are problematic for temporal models of forgetting, but Experiment 3 showed that proactive interference also resisted disruption produced by a secondary task presented within the inter-trial interval. Proactive interference was constantly present and generally resilient to the different manipulations. The combined data suggest a relatively durable, passive representation that can disrupt current working memory under a variety of different circumstances. (shrink)

Spontaneous eye blinks are modulated around perceptual events. Our previous study, using a visual ambiguous stimulus, indicated that blink probability decreases before a reported perceptual switch. In the current study, we tested our hypothesis that an absence of blinks marks a time in which perceptual switches are facilitated in‐ and outside the visual domain. In three experiments, presenting either a visual motion quartet in light or darkness or a bistable auditory streaming stimulus, we found a co‐occurrence of blink (...) rate reduction with increased perceptual switch probability. In the visual domain, perceptual switches induced by a short interruption of visual input (blank) allowed an estimate of the timing of the perceptual event with respect to the motor response. This provided the first evidence that the blink reduction was not a consequence of the perceptual switch. Importantly, by showing that the time between switches and the previous blink was significantly longer than the inter‐blink interval, our studies allowed to conclude that perceptual switches did not happen at random but followed a prolonged period of nonblinking. Correspondingly, blink rate and switch rate showed an inverse relationship. Our study supports the idea that the absence or presence of blinks maps perceptual processes independent of the sensory modality. (shrink)