Single subject analyses reveal consistent recruitment of frontal operculum in performance monitoring.

There are continuing uncertainties regarding whether performance monitoring recruits the anterior insula (aI) and/or the frontal operculum (fO). The proximity and morphological complexity of these two regions make proper identification and isolation of the loci of activation extremely difficult. The use of group averaging methods in human neuroimaging might contribute to this problem. The result has been heterogeneous labeling of this region as aI, fO, or aI/fO, and a discussion of results oriented towards either cognitive or interoceptive functions depending on labeling. In the present article, we adapted the spatial preprocessing of functional magnetic resonance imaging data to account for group averaging artifacts and performed a subject-by-subject analysis in three performance monitoring tasks. Results show that functional activity related to feedback or action monitoring consistently follows local morphology in this region and demonstrate that the activity is located predominantly in the fO rather than in the aI. From these results, we propose that a full understanding of the respective role of aI and fO would benefit from increased spatial resolution and subject-by-subject analysis.

Moving and being moved: differences in cerebral activation during recollection of whole-body motion.

While moving through the world, humans as well as animals can make use of motion cues during both active and passive whole-body motion to track their own position in space. However, the functional neuroanatomy of self-motion processing remains poorly understood. In the present study we aimed to characterize brain networks reflecting whole-body self-motion experience. We used retrieval of previously experienced events, which is known to involve cortical representations of the modalities used to perceive these events. Recollection of self-motion experience may thus engage motor and sensory brain areas, reflecting the active or passive nature of the experienced movement, but may engage also common brain areas processing self-motion. We further compared the retrieval networks of self- and observed motion: even though actual action observation has been shown to recruit brain networks similar to those active during mental simulation, it is unclear to which extent recollection networks of these experiences overlap. Brain activation patterns were recorded using fMRI during mental simulation of recent episodes of (1) experiencing linear whole-body motion (active locomotion and passive transport) and (2) observing another person performing the same tasks. Following the experiential phase, participants recalled the episodes during a MR session. We found that primary sensorimotor brain areas dominate the composition of the recollection network of active walking, while recalling passive transport recruits higher level association areas. Common to both self-motion conditions was activation in the medial temporal lobe. Recollection of self-experienced and observed movement overlapped in motor planning areas. Our results provide evidence that the medial temporal lobe is specifically relevant for retrieval of self-motion information and that motor coding during action observation is reflected in recollection networks.

Physiological Signal Variability in hMT+ Reflects Performance on a Direction Discrimination Task.

Our ability to perceive visual motion is critically dependent on the human motion complex (hMT+) in the dorsal visual stream. Extensive electrophysiological research in the monkey equivalent of this region has demonstrated how neuronal populations code for properties such as speed and direction, and that neurometric functions relate to psychometric functions within the individual monkey. In humans, the physiological correlates of inter-individual perceptual differences are still largely unknown. To address this question, we used functional magnetic resonance imaging (fMRI) while participants viewed translational motion in different directions, and we measured thresholds for direction discrimination of moving stimuli in a separate psychophysics experiment. After determining hMT+ in each participant with a functional localizer, we were able to decode the different directions of visual motion from it using pattern classification (PC). We also characterized the variability of fMRI signal in hMT+ during stimulus and rest periods with a generative model. Relating perceptual performance to physiology, individual direction discrimination thresholds were significantly correlated with the variability measure in hMT+, but not with PC accuracies. Individual differences in PC accuracy were driven by non-physiological sources of noise, such as head-movement, which makes this method a poor tool to investigate inter-individual differences. In contrast, variability analysis of the fMRI signal was robust to non-physiological noise, and variability characteristics in hMT+ correlated with psychophysical thresholds in the individual participants. Higher levels of fMRI signal variability compared to rest correlated with lower discrimination thresholds. This result is in line with theories on stochastic resonance in the context of neuronal populations, which suggest that endogenous or exogenous noise can increase the sensitivity of neuronal populations to incoming signals.

Calcium/calmodulin-dependent protein kinase II mediates group I metabotropic glutamate receptor-dependent protein synthesis and long-term depression in rat hippocampus.

Activation of Group I metabotropic glutamate receptors (mGluRs) in rat hippocampus induces a form of long-term depression (LTD) that is dependent on protein synthesis. However, the intracellular mechanisms leading to the initiation of protein synthesis and expression of LTD after mGluR activation are only partially understood. We investigated the role of several pathways linked to mGluR activation, translation initiation, and induction of LTD. We found that Group I mGluR-dependent protein synthesis and associated LTD, as induced by the agonist (RS)-3,5-dihydrophenylglycine (DHPG) or paired-pulse synaptic stimulation, was dependent on activation of calcium/calmodulin-dependent protein kinase IIα (CaMKII). DHPG induced a transient increase in the level of phospho-CaMKII (phospho-CaMKII(T286)) in synaptoneurosomes prepared from whole hippocampus and in CA1 minislices. In synaptoneurosomes, DHPG also induced an increase in phosphorylation of eIF4E, and an increase in protein synthesis that was abolished by translation inhibitors and the CaMKII inhibitors 1-[N,O-bis(5-isoquinolinesulphonyl)-N-methyl-l-tyrosyl]-4-phenylpiperazine (KN62) and 2-[N-(2-hydroxyethyl)]-N-(4-methoxybenzenesulfonyl)amino-N-(4-chloro-cinnamyl)-N-methylbenzylamine (KN93). In field recordings from CA1, both the translation inhibitor cycloheximide and KN62 significantly reduced DHPG-induced LTD. Combined application did not further reduce the LTD, suggesting a common mechanism. In whole-cell recordings, a third CaMKII inhibitor, AIP (autocamtide-2-related inhibitory peptide), significantly reduced the DHPG-induced LTD of synaptic currents. Inhibition of the classical pathway mediating many Group I mGluR effects by blocking PKC (protein kinase C) or PLC (phospholipase C) did not impair DHPG-induced protein synthesis or LTD. Collectively, these findings demonstrate an important role for CaMKII in mediating the initiation of protein synthesis that then supports the postsynaptic expression of DHPG-induced LTD.

Modality-independent coding of spatial layout in the human brain.

In many nonhuman species, neural computations of navigational information such as position and orientation are not tied to a specific sensory modality [1, 2]. Rather, spatial signals are integrated from multiple input sources, likely leading to abstract representations of space. In contrast, the potential for abstract spatial representations in humans is not known, because most neuroscientific experiments on human navigation have focused exclusively on visual cues. Here, we tested the modality independence hypothesis with two functional magnetic resonance imaging (fMRI) experiments that characterized computations in regions implicated in processing spatial layout [3]. According to the hypothesis, such regions should be recruited for spatial computation of 3D geometric configuration, independent of a specific sensory modality. In support of this view, sighted participants showed strong activation of the parahippocampal place area (PPA) and the retrosplenial cortex (RSC) for visual and haptic exploration of information-matched scenes but not objects. Functional connectivity analyses suggested that these effects were not related to visual recoding, which was further supported by a similar preference for haptic scenes found with blind participants. Taken together, these findings establish the PPA/RSC network as critical in modality-independent spatial computations and provide important evidence for a theory of high-level abstract spatial information processing in the human brain.

Driving dreams: cortical activations during imagined passive and active whole body movement.

It is unclear how subjects perceive and process self-motion cues in virtual reality environments. Movement could be perceived as passive, akin to riding in a car, or active, such as walking down the street. These two very different types of self-motion were studied here using motor imagery in fMRI. In addition, the relative importance of visual and proprioceptive training cues was examined. Stronger activations were found during proprioceptive motor imagery compared with visual motor imagery, suggesting that proprioceptive signals are important for successful imagined movement. No significant activations were found during active movement with proprioceptive training. Passive locomotion, however, was correlated with activity in an occipital-parietal and parahippocampal cortical network, which are the same regions found during navigation with virtual reality stimuli.