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Theta increases with workload and is associated with numerous processes including working memory, problem solving, encoding, or self monitoring. These processes, in turn, involve numerous structures of the brain. However, the relationship between regional brain activity and the occurrence of theta remains unclear. In the present study, simultaneous EEG-fMRI recordings were used to investigate the functional topography of theta. EEG-theta was enhanced by mental arithmetic-induced workload. For the EEG-constrained fMRI analysis, theta-reference time-series were extracted from the EEG, reflecting the strength of theta occurrence during the time course of the experiment. Theta occurrence was mainly associated with activation of the insular cortex, hippocampus, superior temporal areas, cingulate cortex, superior parietal, and frontal areas. Though observation of temporal and insular activation is in accord with the theory that theta specifically reflects encoding processes, the involvement of several other brain regions implies that surface-recorded theta represents comprehensive functional brain states rather than specific processes in the brain. The results provide further evidence for the concept that emergent theta band oscillations represent dynamic functional binding of widely distributed cortical assemblies, essential for cognitive processing. This binding process may form the source of surface-recorded EEG theta.

OBJECTIVE: The quality of averaged gradient artifact subtraction from EEG recorded during fMRI is highly dependent on the accuracy of gradient artifact sampling. Even small sampling shifts (e.g. a single datapoint at 5kHz) increase the variance of the sampled gradient artifacts because of very steep slopes in the signal time course. Hence, although principally gradient artifacts are invariant signals because of their technical origin, variance attributed to sampling errors attenuates the effect of artifact removal. Recently, it has been shown that synchronizing the EEG-amplifier clock to the MR-scanner control-device clock improves artifact reduction by subtraction. METHODS: In order to investigate the synchronized measurement of combined EEG-fMRI, we used simulated EEG by measuring function generator signals in the MR-scanner. Only the usage of known signals allows an assessment of the improvement in accuracy of artifact recording by synchronized compared to non-synchronized measurement, since the signal is identical in both conditions. RESULTS: After averaged gradient artifact subtraction synchronized recorded signals were apparently less distorted than non-synchronized recorded signals. Spectral analyses revealed that especially artifact frequencies above 50Hz had less power in restored synchronized compared to restored non-synchronized recorded signals. Computed total signal variances were not always less in restored synchronized compared to restored non-synchronized recorded signals. CONCLUSIONS: Taken together, synchronizing simultaneous EEG-fMRI measurement is a useful enhancement for averaged gradient artifact subtraction although post-correction filtering is still necessary. SIGNIFICANCE: Our results support the recent finding that synchronization improves the quality of averaged gradient artifact subtraction. However, quantitatively we could not verify a systematic benefit of recording electrical signals during fMRI synchronously rather than non-synchronously to the MR-scanner control-device clock.

The present study examined the neural basis of vivid motor imagery with parametrical functional magnetic resonance imaging. 22 participants performed motor imagery (MI) of six different right-hand movements that differed in terms of pointing accuracy needs and object involvement, i.e., either none, two big or two small squares had to be pointed at in alternation either with or without an object grasped with the fingers. After each imagery trial, they rated the perceived vividness of motor imagery on a 7-point scale. Results showed that increased perceived imagery vividness was parametrically associated with increasing neural activation within the left putamen, the left premotor cortex (PMC), the posterior parietal cortex of the left hemisphere, the left primary motor cortex, the left somatosensory cortex, and the left cerebellum. Within the right hemisphere, activation was found within the right cerebellum, the right putamen, and the right PMC. It is concluded that the perceived vividness of MI is parametrically associated with neural activity within sensorimotor areas. The results corroborate the hypothesis that MI is an outcome of neural computations based on movement representations located within motor areas.

Event-related functional magnetic resonance imaging was applied to identify cortical areas involved in maintaining target information in working memory used for an upcoming grasping action. Participants had to grasp with their thumb and index finger of the dominant right hand three-dimensional objects of different size and orientation. Reaching-to-grasp movements were performed without visual feedback either immediately after object presentation or after a variable delay of 2-12 s. The right inferior parietal cortex demonstrated sustained neural activity throughout the delay, which overlapped with activity observed during encoding of the grasp target. Immediate and delayed grasping activated similar motor-related brain areas and showed no differential activity. The results suggest that the right inferior parietal cortex plays an important functional role in working memory maintenance of grasp-related information. Moreover, our findings confirm the assumption that brain areas engaged in maintaining information are also involved in encoding the same information, and thus extend previous findings on working memory function of the posterior parietal cortex in saccadic behavior to reach-to-grasp movements.

This study addresses the controversy over how motor maps are organized during action simulation by examining whether action simulation states, that is, motor imagery and action observation, run on either effector-specific and/or action-specific motor maps. Subjects had to observe or imagine three types of movements effected by the right hand or the right foot with different action goals. The functional magnetic resonance imaging results showed an action-specific organization within premotor and posterior parietal areas of both hemispheres during action simulation, especially during action observation. There were also less pronounced effector-specific activation sites during both simulation processes. It is concluded that the premotor and parietal areas contain multiple motor maps rather than a single, continuous map of the body. The forms of simulation (observation, imagery), the task contexts (movements related to an object, with usual/unusual effector), and the underlying reason for performing the simulation (rate your subjective success afterwards) lead to the specific use of different representational motor maps within both regions. In our experimental setting, action-specific maps are dominant especially, during action observation, whereas effector-specific maps are recruited to only a lesser degree.

Jeannerod (2001) hypothesized that action execution, imagery, and observation are functionally equivalent. This led to the major prediction that these motor states are based on the same action-specific and even effector-specific motor representations. The present study examined whether hand and foot movements are represented in a somatotopic manner during action execution, imagery, and action observation. The experiment contained ten conditions: three execution conditions, three imagery conditions, three observation conditions, and one baseline condition. In the nine experimental conditions, participants had to execute, observe, or imagine right-hand extension/flexion movements or right-foot extension/flexion movements. The fMRI results showed a somatotopic organization within the contralateral premotor and primary motor cortex during motor imagery and motor execution. However, there was no clear somatotopic organization of action observation in the given regions of interest within the contralateral hemisphere, although observation of these movements activated these areas significantly.

The perception of action is influenced by the observer's familiarity with its movement. However, how does motor familiarity with own movement patterns modulate the visual perception of action effects? Cortical activation was examined with fMRI while 20 observers were watching videotaped point-light displays of markers on the shoulders, the right elbow, and wrist of an opposing table tennis player. The racket and ball were not displayed. Participants were asked to predict the invisible effect of the stroke, that is, the ball flight direction. Different table tennis models were used without the observers knowing and being informed in advance that some of the presented videos displayed their own movements from earlier training sessions. Prediction had to be made irrespective of the identity of the player represented by the four moving markers. Results showed that participants performed better when observing their "own" strokes. Using a region-of-interest approach, fMRI data showed that observing own videos was accompanied by stronger activation (compared to other videos) in the left angular gyrus of the inferior parietal lobe and the anterior rostral medial frontal cortex. Other videos elicited stronger activation than own videos in the left intraparietal sulcus and right supramarginal gyrus. We suggest that during action observation of motorically familiar movements, the compatibility between the observed action and the observers' motor representation is already coded in the parietal angular gyrus--in addition to the paracingulate gyrus. The activation in angular gyrus is presumably part of an action-specific effect retrieval that accompanies actor-specific prefrontal processing. The intraparietal sulcus seems to be sensitive to incongruence between observed kinematics and internal model representations, and this also influences processing in the supramarginal gyrus.