Response-Modality-Specific Encoding of Human Choices in Upper Beta Band Oscillations during Vibrotactile Comparisons

Perceptual decisions based on the comparison of two vibrotactile frequencies have been extensively studied in non-human primates. Recently, we obtained corresponding findings from human oscillatory electroencephalography (EEG) activity in the form of choice-selective modulations of upper beta band amplitude in medial premotor areas. However, the research in non-human primates as well as its human counterpart was so far limited to decisions reported by button presses. Thus, here we investigated whether the observed human beta band modulation is specific to the response modality. We recorded EEG activity from participants who compared two sequentially presented vibrotactile frequencies (f1 and f2), and decided whether f2 > f1 or f2 < f1, by performing a horizontal saccade to either side of a computer screen. Contrasting time-frequency transformed EEG data between both choices revealed that upper beta band amplitude (∼24–32 Hz) was modulated by participants’ choices before actual responses were given. In particular, “f2 > f1” choices were always associated with higher beta band amplitude than “f2 < f1” choices, irrespective of whether the choice was correct or not, and independent of the specific association between saccade direction and choice. The observed pattern of beta band modulation was virtually identical to our previous results when participants responded with button presses. In line with an intentional framework of decision making, the most likely sources of the beta band modulation were now, however, located in lateral as compared to medial premotor areas including the frontal eye fields. Hence, we could show that the choice-selective modulation of upper beta band amplitude is on the one hand consistent across different response modalities (i.e., same modulation pattern in similar frequency band), and on the other hand effector specific (i.e., modulation originating from areas involved in planning and executing saccades)

Gamma and Beta Oscillations in Human MEG Encode the Contents of Vibrotactile Working Memory

Ample evidence suggests that oscillations in the beta band represent quantitative information about somatosensory features during stimulus retention. Visual and auditory working memory (WM) research, on the other hand, has indicated a predominant role of gamma oscillations for active WM processing. Here we reconciled these findings by recording whole-head magnetoencephalography during a vibrotactile frequency comparison task. A Braille stimulator presented healthy subjects with a vibration to the left fingertip that was retained in WM for comparison with a second stimulus presented after a short delay. During this retention interval spectral power in the beta band from the right intraparietal sulcus and inferior frontal gyrus (IFG) monotonically increased with the to-be-remembered vibrotactile frequency. In contrast, induced gamma power showed the inverse of this pattern and decreased with higher stimulus frequency in the right IFG. Together, these results expand the previously established role of beta oscillations for somatosensory WM to the gamma band and give further evidence that quantitative information may be processed in a fronto-parietal network

Grundlagen perzeptueller Entscheidungen: Erkenntnisse aus einer somatosensorischen Vergleichsaufgabe

Navigating through everyday life requires deciding between alternatives almost constantly: For instance, ’Should I wear a pair of Jeans or chinos?’ or ’Should I have coffee or tea?’ etc. The simplest form of decisions we face is based on sensory information only, e.g., when we need to decide whether we can drink the cup of hot coffee in our hands just now, or whether we should wait a couple of more minutes. Such purely sensory-driven decisions, which fall into the domain of perceptual decision making, constitute a prime example for studying the neural processes that are involved in the transformation of sensory information into behavior. In other words, the simplistic nature of perceptual decision making is often exploited in neuroscience to understand the principles of decision making in general. Over the last decades, especially electrophysiological recordings in animals have fostered the understanding of the involved neural processes. The according findings suggested that decisions are formed as intentions to act in those brain structures, which also implement the ensuing behavior. In particular, this implicated a fronto-parietal network of cortical areas. The work presented here aimed at linking these insights from animal research to electroencephalogram (EEG) recordings in humans. In particular, we investigated the EEG signal during a simple task in which participants compared the frequencies of two vibrations that were sequentially presented to their index finger. In four studies, comprising six experiments employing this simple comparison task, we demonstrated that the findings from invasive animal recordings can be directly related to non-invasive human scalp recordings, and moreover, can even be extended to previously unexplored decision contexts. That is, depending on response modality and decision rule, we found a choice- indicative signal originating from those structures that implemented the consequences of the comparison task, notably, implicating the same fronto- parietal network as suggested by animal research. Moreover, we identified a fine-grained evidence signal in parietal areas that was previously known from other perceptual decision making tasks, however, has never been reported in a sequential comparison task. Interestingly, by using a comparison task, we could reveal that the parietal evidence signal appears to convey more information than assumed before, inviting for speculations about whether current theories of perceptual decision making might actually be extended to a more general framework of magnitude estimation.Im täglichen Leben müssen wir uns fast ununterbrochen zwischen möglichen Optionen entscheiden: z.B. ‘Soll ich eine Jeans oder eine Chino tragen?’ oder ‘Soll ich einen Kaffee oder einen Tee trinken?’ usw. Die einfachste Form einer solchen Entscheidung betrifft Entscheidungen, die ausschließlich auf Grund von sensorischen Reizen getroffen werden. Wenn wir z.B. entscheiden müssen, ob wir die heiße Tasse Kaffee, die wir gerade in Händen halten, sofort trinken können oder ob wir sie besser noch etwas abkühlen lassen sollten. Solche rein sensorisch getriebenen Entscheidungen werden als perzeptuelle Entscheidungen bezeichnet und liefern ausgezeichnete Rahmenbedingungen, um die neuronalen Prozesse zu untersuchen, die einer Umwandlung von sensorischen Reizen in willentliche Handlungen zu Grunde liegen. Anders ausgedrückt, in den Neurowissenschaften wird die Einfachheit von perzeptuellen Entscheidungen oftmals dazu genutzt, um die Grundlagen von Entscheidungen im Allgemeinen zu verstehen. In den letzten Jahrzenten haben gerade elektrophysiologische Daten aus Tierversuchen unser Verständnis von den zugrundeliegenden neuronalen Prozessen vorangetrieben. Die Resultate aus dieser Forschung implizieren, dass Entscheidungen als Handlungsabsichten implementiert sind; und zwar in den Hirnregionen, die auch für die Ausführung der resultierenden Handlung zuständig sind. Insbesondere beinhaltet dies ein fronto-parietales kortikales Netzwerk. In den hier vorgestellten Arbeiten versuchen wir, diese aus Tierversuchen gewonnen Einsichten, direkt mit dem vom Menschen abgeleiteten Elektroenzephalogram (EEG) in Verbindung zu bringen. Dazu haben wir das EEG Signal während eines Vergleichs zweier nacheinander präsentierter Vibrationen untersucht. In vier Studien, die insgesamt sechs Experimente mit dieser einfachen Vergleichsaufgabe beinhalten, konnten wir zeigen, dass die Erkenntnisse, die man aus Tierversuchen gewonnen hat, übereinstimmend auch aus menschlichen EEG Signalen abgeleitet werden können und, darüber hinaus, sogar auf bis dato unerforschte Entscheidungen übertragen werden können. Im Einzelnen bedeutet dies, dass je nachdem wie die Teilnehmer unserer Experimente ihre Entscheidung mitteilen mussten, bzw. je nachdem welche Entscheidungsregel sie anwenden mussten, ein EEG Korrelat gefunden wurde, welches nicht nur die Entscheidung der Teilnehmer widergespiegelt hat, sondern jeweils auch den Hirnarealen zugeordnet werden konnte, die für die Umsetzung der entsprechenden Entscheidungskonsequenz zuständig waren. Beachtenswert hierbei ist außerdem, dass diese Hirnregionen demselben fronto-parietalen Netzwerk entsprachen, welches auch in Tierversuchen identifiziert wurde. Darüber hinaus konnten wir zum ersten Mal ein detailliertes Evidenzsignal in parietalen Hirnarealen nachweisen, welches zwar aus anderen perzeptuellen Entscheidungsstudien bekannt ist, allerdings noch nie zuvor in einer Vergleichsaufgabe berichtet wurde. Interessanterweise hat uns die Anwendung einer solchen Vergleichsaufgabe zusätzlich ermöglicht, zu zeigen, dass eben jenes parietale Evidenzsignal scheinbar mehr Informationen beinhaltet als bisher angenommen. Diese Einsicht lädt wiederum zu Spekulationen ein, ob gegenwärtige Theorien zu perzeptuellen Entscheidungen womöglich weiter generalisiert werden können und zu einem globalen Konzept zur Schätzung von Größenordnungen im Allgemeinen erweitert werden können

Gamma and Beta Oscillations in Human MEG Encode the Contents of Vibrotactile Working Memory

Ample evidence suggests that oscillations in the beta band represent quantitative information about somatosensory features during stimulus retention. Visual and auditory working memory (WM) research, on the other hand, has indicated a predominant role of gamma oscillations for active WM processing. Here we reconciled these findings by recording whole-head magnetoencephalography during a vibrotactile frequency comparison task. A Braille stimulator presented healthy subjects with a vibration to the left fingertip that was retained in WM for comparison with a second stimulus presented after a short delay. During this retention interval spectral power in the beta band from the right intraparietal sulcus and inferior frontal gyrus (IFG) monotonically increased with the to-be-remembered vibrotactile frequency. In contrast, induced gamma power showed the inverse of this pattern and decreased with higher stimulus frequency in the right IFG. Together, these results expand the previously established role of beta oscillations for somatosensory WM to the gamma band and give further evidence that quantitative information may be processed in a fronto-parietal network