Contribution of the superior colliculus to error correction in the skeletomotor system

Während der Ausführung von Armbewegungen durch einen Primaten wurden elektrophysiologische Einzelzellableitungen im Colliculus superior des Versuchstieres vorgenommen. Der Versatz des Bewegungszieles in Koinzidenz mit dem Beginn der Armbewegung ermöglicht einen Vergleich zwischen der armkorrekturbedingten Änderung der neuronalen Entladungsrate und der einhergehenden kinematischen Veränderung. Hier zeigt sich eine unspezifische neuronale Antwort, die auf Modulation der Amplitude, der Dauer und des Beginns beruht, und nicht mit bisherigen Ergebnissen aus Ableitungen im primären Motorkortex und Parietalkortex in Deckung gebracht werden kann. Die colliculären Antworten zeigen nach 89°ms (Vorzugsrichtung) und 99°ms (Nicht-Vorzugsrichtung) signifikante Abweichungen gegenüber Kontrollbedingungen, und stellen die kürzesten neuronalen Latenzen in der Literatur. Mit Bezug auf die kinematischen Änderungen ergibt sich somit die Möglichkeit der funktionalen Steuerung von schnellen Armkorrekturen.The experiments reveal neuronal responses during the correction of arm movements in the superior colliculus of the macaque monkey while it performed various reach-fixation tasks. When compared to unperturbed control movements the nonspecific spike rate aberrations of reach-related cells in the intermediate to deep collicular layers are caused by the modulation of amplitude, discharge duration and onset, thus are substantially different to the assembly-like pattern reported for neuronal responses in the primary motor cortex and the posterior parietal cortex. The shortest neuronal latencies to reach correction in literature are found in the collicular responses at hand, with shorter latencies for corrections into preferred (median: 89°ms) than non-preferred (median: 99°ms) directions. With respect to the onset of kinematic alterations during the correction of arm movements this proposes the possibility of a functional collicular contribution to skeletomotor actions

Enhancing effects of NMDA-receptor blockade on extinction learning and related brain activation are modulated by BMI

A distributed network including prefrontal and hippocampal regions is involved in context-related extinction learning as well as in renewal. Renewal describes the recovery of an extinguished response if the context of extinction differs from the context of recall. Animal studies have demonstrated that prefrontal, but not hippocampal $\it N$-methyl-$\it D$-aspartate receptor (NMDAR) antagonism disrupted extinction learning and processing of task context. However, human studies of NMDAR in extinction learning are lacking, while NMDAR antagonism yielded contradictory results in other learning tasks. This fMRI study investigated the role of NMDAR for human behavioral and brain activation correlates of extinction and renewal. Healthy volunteers received a single dose of the NMDAR antagonist memantine prior to extinction of previously acquired stimulus-outcome associations presented in either identical or novel contexts. We observed better, and partly faster, extinction learning in participants receiving the NMDAR antagonist compared to placebo. However, memantine did not affect renewal. In both extinction and recall, the memantine group showed a deactivation in extinction-related brain regions, particularly in the prefrontal cortex, while hippocampal activity was increased. This higher hippocampal activation was in turn associated with the participants' body mass index (BMI) and extinction errors. Our results demonstrate potentially dose-related enhancing effects of memantine and highlight involvement of hippocampal NMDAR in context-related extinction learning

Cerebellar‐hippocampal processing in passive perception of visuospatial change

In addition to its role in visuospatial navigation and the generation of spatial representations, in recent years, the hippocampus has been proposed to support perceptual processes. This is especially the case where high‐resolution details, in the form of fine‐grained relationships between features such as angles between components of a visual scene, are involved. An unresolved question is how, in the visual domain, perspective‐changes are differentiated from allocentric changes to these perceived feature relationships, both of which may be argued to involve the hippocampus. We conducted functional magnetic resonance imaging of the brain response (corroborated through separate event‐related potential source‐localization) in a passive visuospatial oddball‐paradigm to examine to what extent the hippocampus and other brain regions process changes in perspective, or configuration of abstract, three‐dimensional structures. We observed activation of the left superior parietal cortex during perspective shifts, and right anterior hippocampus in configuration‐changes. Strikingly, we also found the cerebellum to differentiate between the two, in a way that appeared tightly coupled to hippocampal processing. These results point toward a relationship between the cerebellum and the hippocampus that occurs during perception of changes in visuospatial information that has previously only been reported with regard to visuospatial navigation

Distraction by a cognitive task has a higher impact on electrophysiological measures compared with conditioned pain modulation

$\bf Background$ Conditioned pain modulation (CPM) evaluates the effect of a painful conditioning stimulus (CS) on a painful test stimulus (TS). Using painful cutaneous electrical stimulation (PCES) as TS and painful cold water as CS, the pain relief was paralleled by a decrease in evoked potentials (PCES-EPs). We now aimed to compare the effect of CPM with cognitive distraction on PCES-induced pain and PCES-EP amplitudes. $\bf Methods$ PCES was performed using surface electrodes inducing a painful sensation of 60 (NRS 0–100) on one hand. In a crossover design healthy subjects (included: n = 38, analyzed: n = 23) immersed the contralateral hand into 10 °C cold water (CS) for CPM evaluation and performed the 1-back task for cognitive distraction. Before and during the CS and 1-back task, respectively, subjects rated the pain intensity of PCES and simultaneously cortical evoked potentials were recorded. $\bf Results$ Both CPM and cognitive distraction significantly reduced PCES-EP amplitudes (CPM: 27.6 $\pm$ 12.0 $\mu$V to 20.2 $\pm$ 9.5 $\mu$V, cognitive distraction: 30.3 $\pm$ 14.2 $\mu$V to 13.6 $\pm$ 5.2 $\mu$V, p < 0.001) and PCES-induced pain (on a 0–100 numerical rating scale: CPM: 58 $\pm$ 4 to 41.1 $\pm$ 12.3, cognitive distraction: 58.3 $\pm$ 4.4 to 38.0 $\pm$ 13.0, p < 0.001), though the changes in pain intensity and PCES-amplitude did not correlate. The changes of the PCES-EP amplitudes during cognitive distraction were more pronounced than during CPM (p = 0.001). $\bf Conclusions$ CPM and cognitive distraction reduced the PCES-induced pain to a similar extent. The more pronounced decrease of PCES-EP amplitudes after distraction by a cognitive task implies that both conditions might not represent the general pain modulatory capacity of individuals, but may underlie different neuronal mechanisms with the final common pathway of perceived pain reduction