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.

Anticipatory changes in human motoneuron discharge patterns during motor preparation.

The influence of motor preparation on human motoneuron activity was studied by combining single motor unit recording techniques with reaction-time (RT) methods. The tonic activity of wrist extensor motor units associated with voluntary isometric contractions was analysed during preparation for a ballistic wrist extensor muscle contraction, using a time preparation procedure. Two durations of the preparatory period elapsing between the warning signal and the response signal were used in separate blocks of trials: a short preparatory period (1 s) allowing optimum time preparation, and a longer, non-optimum one (3 s). Changes in motoneuron tonic discharge patterns not associated with any changes in the force output were observed during the preparatory period, which suggests that these changes were subtle enough to prevent any changes in muscle contraction from occurring before the forthcoming movement. The changes observed were a lengthening of the mean interspike interval (ISI) and a decrease in the ISI variability. These data confirm that inhibitory mechanisms are activated during motor preparation and suggest that spinal inhibitory mechanisms are involved in the preparatory processes. The mechanisms possibly involved, such as presynaptic inhibition, disfacilitation processes or AHP conductance changes, are discussed. The fact that the preparation-induced effects on motoneuron activity were particularly prominent during the last part of the 3 s preparatory period suggests that they were probably related to the neural processes underlying temporal estimation. The anticipatory changes in motoneuron activity observed here during preparation for action provide evidence that central influences act on spinal motoneurons well before it is time to act.

Single-trial analysis of oddball event-related potentials in simultaneous EEG-fMRI.

There has recently been a growing interest in the use of simultaneous electroencephalography (EEG) and functional MRI (fMRI) for evoked activity in cognitive paradigms, thereby obtaining functional datasets with both high spatial and temporal resolution. The simultaneous recording permits obtaining event-related potentials (ERPs) and MR images in the same environment, conditions of stimulation, and subject state; it also enables tracing the joint fluctuations of EEG and fMRI signals. The goal of this study was to investigate the possibility of tracking the trial-to-trial changes in event-related EEG activity, and of using this information as a parameter in fMRI analysis. We used an auditory oddball paradigm and obtained single-trial amplitude and latency features from the EEG acquired during fMRI scanning. The single-trial P300 latency presented significant correlation with parameters external to the EEG (target-to-target interval and reaction time). Moreover, we obtained significant fMRI activations for the modulation by P300 amplitude and latency, both at the single-subject and at the group level. Our results indicate that, in line with other studies, the EEG can bring a new dimension to the field of fMRI analysis by providing fine temporal information on the fluctuations in brain activity.

[Treatment dynamics in sensorimotor disorders: the contribution of electrophysiology]. / Dynamique du traitement de l'information sensorimotrice: apport de l'électrophysiologie.

In the field of sensorimotor activities, progresses achieved over the last fifty years have been largely driven by the Reaction Time (RT) paradigm. Information processing models are set in the context of a global breakdown of sensorimotor activities in multiple concatenated stages, each aggregated in many fundamental operations that are functionally linked. If there is a consensus today about this breakdown, the way stages organize themselves in time however is still much debated. According to one hypothesis, there is no temporal overlap between each stages: the process occurs sequentially. According to another theory, the stages overlap over in time: the process occurs in a parallel manner. A behavioral analysis does not allow to determine between these two hypothesis because the RT represents the final product of the whole sensorimotor pathway, while the temporal organization of the processing of information depends on the nature of the transfer between individual stages. An all-or-nothing information transfer, also called discrete, leads to a sequential organization, while a progressive or continuous transfer brings about a parallel organization. Moreover, contrary to a preconceived notion, data obtained from classical neurophysiology are compatible with both a sequential organization and a parallel organization. Particularly, the great number of connections between the different elements of the nervous system has often seemed difficult to conciliate with a sequential organization. In fact, this argument is inadmissible because it stems from confusion between a temporal organization and an anatomical organization of the processing of information. More generally, our knowledge of the functional anatomy of sensorimotor activities imposes but few constraints on the temporal organization patterns of the processing of information. The lack of interest for the neurophysiological argument seems essentially due to the fact that theses arguments rest on research which is not aimed at the temporal organization of the sensorimotor information processing. Recently, approaches that integrate concepts and methods used in experimental psychology and neurosciences have contributed to putting in perspective the organization of information processing. Electromyography, EEG, reflexology and neuronal recording techniques have been used in the context of two inference logics. The first logic, that we call "factual", is based on the study of functional relations between RT and certain neuronal events. The second logic, that we call "chronometric", is based on the study of the relationships between RT and intervals resulting from the breakdown of the RT in relation to certain neuronal events. Generally speaking, most studies suggest that in tasks where the stimulus is composed of numerous attributes, information processing operates in parallel. On the other hand, when the stimulus is made up of a single attribute, information processing could be operating in a sequential manner. One weakness of this electrophysiological approach is that it has so far only examined relationships between physiological indicators and means RT. We propose here to offset these weaknesses by examining functional relationships between RT distribution variances and certain neuronal events linked to information processing.