MP Deiber - Academia.edu (original) (raw)

Papers by MP Deiber

Research paper thumbnail of Organisation temporelle de la motricité séquentielle unimanuelle et bimanuelle

Research paper thumbnail of Functional magnetic resonance imaging evidence for comparable cerebral networks in motor preparation and execution

Research paper thumbnail of Cerebral structures participating in motor preparation in humans: a positron emission tomography study

Journal of Neurophysiology

1. Using positron emission tomography and measurement of regional cerebral blood flow (rCBF) as a... more 1. Using positron emission tomography and measurement of regional cerebral blood flow (rCBF) as an index of cerebral activity we investigated the central processing of motor preparation in 13 healthy volunteers. 2. We used a motor reaction time paradigm with visual cues as preparatory and response signals. A preparatory stimulus (PS) provided either full, partial, or no information regarding two variables of a forthcoming right finger movement: finger type (index or little finger) and movement direction (abduction or elevation). After a variable delay period, a response stimulus (RS) prompted the movement. A condition was also tested in which the subject could freely select any of the four possible movements during the preparation period ("free" condition). The timing of events was designed to emphasize the motor preparation phase over the motor execution component during the scanning time of 1 min. 3. Distinct preparatory processes, which depended on the information conta...

Research paper thumbnail of Regional cerebral blood flow during voluntary arm and hand movements in human subjects

Journal of neurophysiology, 1991

1. Regional cerebral blood flow (rCBF) was measured using positron emission tomography in six nor... more 1. Regional cerebral blood flow (rCBF) was measured using positron emission tomography in six normal volunteers while at rest and while performing four different repetitive movements of the right arm. 2. The four movements were performed in random order and consisted of abduction of the index finger, making a fist, sequential thumb to digit opposition, and shoulder flexion. All the movements were done at the same rate, using an auditory cue and involved displacements through similar amounts of the physiological range at each joint. 3. Increases in rCBF were interpreted as evidence of local neural activation and all four movements were associated with significant increases in CBF in the contralateral sensorimotor and premotor areas and in the supplementary motor area (SMA). 4. The average increase in blood flow in the contralateral sensorimotor cortex was significantly greater for the shoulder movement (31%) than for the three other movements. The increases with finger opposition (21...

Research paper thumbnail of Mesial motor areas in self-initiated versus externally triggered movements examined with fMRI: effect of movement type and rate

Journal of neurophysiology, 1999

The human frontomesial cortex reportedly contains at least four cortical areas that are involved ... more The human frontomesial cortex reportedly contains at least four cortical areas that are involved in motor control: the anterior supplementary motor area (pre-SMA), the posterior SMA (SMA proper, or SMA), and, in the anterior cingulate cortex, the rostral cingulate zone (RCZ) and the caudal cingulate zone (CCZ). We used functional magnetic resonance imaging (fMRI) to examine the role of each of these mesial motor areas in self-initiated and visually triggered movements. Healthy subjects performed self-initiated movements of the right fingers (self-initiated task, SI). Each movement elicited a visual signal that was recorded. The recorded sequence of visual signals was played back, and the subjects moved the right fingers in response to each signal (visually triggered task, VT). There were two types of movements: repetitive (FIXED) or sequential (SEQUENCE), performed at two different rates: SLOW or FAST. The four regions of interest (pre-SMA, SMA, RCZ, CCZ) were traced on a high-resol...

Research paper thumbnail of Frontal and parietal networks for conditional motor learning: a positron emission tomography study

Journal of neurophysiology, 1997

Studies on nonhuman primates show that the premotor (PM) and prefrontal (PF) areas are necessary ... more Studies on nonhuman primates show that the premotor (PM) and prefrontal (PF) areas are necessary for the arbitrary mapping of a set of stimuli onto a set of responses. However, positron emission tomography (PET) measurements of regional cerebral blood flow (rCBF) in human subjects have failed to reveal the predicted rCBF changes during such behavior. We therefore studied rCBF while subjects learned two arbitrary mapping tasks. In the conditional motor task, visual stimuli instructed which of four directions to move a joystick (with the right, dominant hand). In the evaluation task, subjects moved the joystick in a predetermined direction to report whether an arrow pointed in the direction associated with a given stimulus. For both tasks there were three rules: for the nonspatial rule, the pattern within each stimulus determined the correct direction; for the spatial rule, the location of the stimulus did so; and for the fixed-response rule, movement direction was constant regardless...

Research paper thumbnail of Sequential mapping favours the hypothesis of distinct generators for Na and Pa middle latency auditory evoked potentials

Electroencephalography and clinical neurophysiology

The temporo-spatial organization of Na and Pa middle latency auditory components evoked by monaur... more The temporo-spatial organization of Na and Pa middle latency auditory components evoked by monaural clicks delivered separately to right and left ears was assessed by sequential mapping of scalp potentials. The potential field distribution was found to be different for the two components and was assessed by calculating the maximal potential differences in the Na/Pa time period. These data are compatible with the hypothesis that distinct generators are responsible for the two components. Scalp potential field configuration observed for Na suggests a deep generator, which could be situated at the mesencephalic or diencephalic level. Bilateral cortical generators tangentially orientated satisfactorily account for the distribution of the Pa potential field, which could be related to simultaneous activation of both supratemporal auditory cortices in response to monaural stimulation.

Research paper thumbnail of LP1: Aging effects on EEG alpha activity during internal and external motor sequence generation

Clinical Neurophysiology, 2014

Question: The creation of conscious and meaningful perceptions from sensory information should be... more Question: The creation of conscious and meaningful perceptions from sensory information should be fast and action-guiding. This requires fast integration of stimulus-driven activity with endogenous processes, such as prior experiences and intentions. A flexible mechanism may increase the impact of endogenous processes when the quality of the sensory information is poor or inconclusive. Visual illusions, such as visual ambiguity, provide a tool to investigate the brain response when the sensory information available is largely inconclusive for the generation of a meaningful percept. Methods: The EEG response during ambiguous and unambiguous perception was measured in twelve participants. Artefact-free epochs were extracted and the oscillatory theta response was extracted for all epochs using a single Morlet wavelet of six cycles and a centre frequency of 5.5 Hz (approximate frequency range: 4 to 7 Hz). Results: The EEG theta response was larger at frontal than at occipital regions in all of our twelve participants when the stimulus was ambiguous. This pattern was not found during unambiguous perception. Perceptual switches lead to an overall increase of theta activity. Conclusions: This outcome indicates that the contribution of endogenous processes on perception is variable. Anterior theta activity is specifically important for coherent perception when sensory information is ambiguous or inconclusive. Flexibility of endogenous processes may be a general phenomenon adjusting neural communication strategies on task demands (see also Mathes et al., 2012, Psychophysiology).

Research paper thumbnail of P395: Switching from bimanual to unimanual tapping reveals two distinct post-switching beta synchronization processes

Clinical Neurophysiology, 2014

Research paper thumbnail of Neural networks for braille reading by the blind include visual cortex

Research paper thumbnail of Decomposition and evaluation of activity in multiple event-related trials

IEEE 12th International Conference on BioInformatics and BioEngineering, BIBE 2012, 2012

ABSTRACT It is generally accepted that evoked and induced activations represent different aspects... more ABSTRACT It is generally accepted that evoked and induced activations represent different aspects of cerebral functions during an Event Related Potentials (ERP) experiment. Independent Component Analysis (ICA) has been successfully applied to event related electroencephalography (EEG) to decompose it into a sum of spatially fixed and temporally independent components that can be attributed to underlying cortical activity. A major problem in the application of ICA is the stability of estimated independent components. In this paper we exploited the split-half approach to assess component stability. We used different measures quantifying both phase and energy aspects of the ERP, in order to distinguish evoked from induced oscillations. We applied these measures to the stable independent components derived from a dataset of progressive Mild Cognitive Impairment (PMCI) and elderly controls. We found reduced energy in the induced theta activity in PMCI subjects, in accordance with previous studies. In addition, PMCI subjects presented lower phase-locking values and diminished late alpha band energy in contrast to controls.

Research paper thumbnail of The Color Center in the Cerebral-Cortex of Man

Research paper thumbnail of Working memory load-related electroencephalographic parameters can differentiate progressive from stable mild cognitive impairment

Neuroscience, 2007

Recent studies described several changes of endogenous event-related potentials (ERP) and brain r... more Recent studies described several changes of endogenous event-related potentials (ERP) and brain rhythm synchronization during memory activation in patients with Alzheimer's disease (AD). To examine whether memory-related EEG parameters may predict cognitive decline in mild cognitive impairment (MCI), we assessed P200 and N200 latencies as well as beta event-related synchronization (ERS) in 16 elderly controls (EC), 29 MCI cases and 10 patients with AD during the successful performance of a pure attentional detection task as compared with a highly working memory demanding two-back task. At 1 year follow-up, 16 MCI patients showed progressive cognitive decline (PMCI) and 13 remained stable (SMCI). Both P200 and N200 latencies in the two-back task were longer in PMCI and AD cases compared with EC and SMCI cases. During the interval 1000 ms to 1700 ms after stimulus, beta ERS at parietal electrodes was of lower amplitude in PMCI and AD compared with EC and SMCI cases. Univariate models showed that P200, N200 and log% beta values were significantly related to the SMCI/PMCI distinction with areas under the receiver operating characteristic curve of 0.93, 0.78 and 0.72, respectively. The combination of all three EEG hallmarks was the stronger predictor of MCI deterioration with 90% of correctly classified MCI cases. Our data reveal that PMCI and clinically overt AD share the same pattern of working memory-related EEG activation characterized by increased P200-N200 latencies and decreased beta ERS. They also show that P200 latency during the two-back task may be a simple and promising EEG marker of rapid cognitive decline in MCI.

Research paper thumbnail of A controlled positron emission tomography study of obsessive and neutral auditory stimulation in obsessive-compulsive disorder with checking rituals

Psychiatry Research, 1996

Research paper thumbnail of Electrical stimulation of precentral cortical area in the treatment of central pain: electrophysiological and PET study

Research paper thumbnail of Deficient activation of the motor cortical network in patients with writer's cramp

Neurology, 1999

... The decreased activation in sensorimotor cortex during the sustained contraction in writer&#x... more ... The decreased activation in sensorimotor cortex during the sustained contraction in writer's cramppatients is not ... detect functional relations between different brain structures in the absence of tangible activation.45 In writer's cramp patients, the reduced putaminal correlations ...

Research paper thumbnail of Changes of middle latency auditory evoked potentials during natural sleep in humans

Neurology, 1989

During natural nocturnal sleep, Na and Pa middle latency auditory evoked potentials (MLAEPs) unde... more During natural nocturnal sleep, Na and Pa middle latency auditory evoked potentials (MLAEPs) underwent significant variations which were related to sleep stages. The deepening of sleep from stage II to stage IV was paralleled by a latency shift and an amplitude decrease of Na and Pa, while MLAEPs were similar in wakefulness and REM sleep. Moreover, Na and Pa components tended to shift over the hemisphere contralateral to the stimulated ear during sleep. These findings demonstrate that the responsiveness of the auditory cortex to acoustic stimuli is modulated during sleep. Vigilance should be monitored during MLAEP recordings in patients.

Research paper thumbnail of Gender Difference in Premotor Activity during Active Tactile Discrimination

NeuroImage, 2000

To investigate possible gender differences in tactile discrimination tasks, we measured cerebral ... more To investigate possible gender differences in tactile discrimination tasks, we measured cerebral blood flow of seven men and seven women using positron emission tomography and (15)O water during tactile tasks performed with the right index finger. A nondiscrimination, somatosensory control task activated the left primary sensorimotor cortex and the left parietal operculum extending to the posterior insula without any gender difference. Compared with the control task, discrimination tasks activated the superior and inferior parietal lobules bilaterally, right dorsal premotor cortex, and dorsolateral prefrontal cortex in both genders, consistent with the notion of right hemisphere involvement during exploratory attentional movements. In both genders, symmetric activation of the superior and inferior parietal lobules and asymmetric activation of the right dorsolateral prefrontal cortex were confirmed. The former is consistent with the spatial representation of the tactile input and the latter with the spatial working memory. However, activation of the dorsal premotor cortex was asymmetric in men, whereas it was symmetric in women, the gender difference being statistically significant. This may suggest gender differences in motor programs for exploration in manipulospatial tasks such as tactile discrimination with active touch, possibly by greater interhemispheric interaction through the dorsal premotor cortices in women than in men.

Research paper thumbnail of Cerebral Processes Related to Visuomotor Imagery and Generation of Simple Finger Movements Studied with Positron Emission Tomography

Research paper thumbnail of Broca's area and mental preparation

Research paper thumbnail of Organisation temporelle de la motricité séquentielle unimanuelle et bimanuelle

Research paper thumbnail of Functional magnetic resonance imaging evidence for comparable cerebral networks in motor preparation and execution

Research paper thumbnail of Cerebral structures participating in motor preparation in humans: a positron emission tomography study

Journal of Neurophysiology

1. Using positron emission tomography and measurement of regional cerebral blood flow (rCBF) as a... more 1. Using positron emission tomography and measurement of regional cerebral blood flow (rCBF) as an index of cerebral activity we investigated the central processing of motor preparation in 13 healthy volunteers. 2. We used a motor reaction time paradigm with visual cues as preparatory and response signals. A preparatory stimulus (PS) provided either full, partial, or no information regarding two variables of a forthcoming right finger movement: finger type (index or little finger) and movement direction (abduction or elevation). After a variable delay period, a response stimulus (RS) prompted the movement. A condition was also tested in which the subject could freely select any of the four possible movements during the preparation period ("free" condition). The timing of events was designed to emphasize the motor preparation phase over the motor execution component during the scanning time of 1 min. 3. Distinct preparatory processes, which depended on the information conta...

Research paper thumbnail of Regional cerebral blood flow during voluntary arm and hand movements in human subjects

Journal of neurophysiology, 1991

1. Regional cerebral blood flow (rCBF) was measured using positron emission tomography in six nor... more 1. Regional cerebral blood flow (rCBF) was measured using positron emission tomography in six normal volunteers while at rest and while performing four different repetitive movements of the right arm. 2. The four movements were performed in random order and consisted of abduction of the index finger, making a fist, sequential thumb to digit opposition, and shoulder flexion. All the movements were done at the same rate, using an auditory cue and involved displacements through similar amounts of the physiological range at each joint. 3. Increases in rCBF were interpreted as evidence of local neural activation and all four movements were associated with significant increases in CBF in the contralateral sensorimotor and premotor areas and in the supplementary motor area (SMA). 4. The average increase in blood flow in the contralateral sensorimotor cortex was significantly greater for the shoulder movement (31%) than for the three other movements. The increases with finger opposition (21...

Research paper thumbnail of Mesial motor areas in self-initiated versus externally triggered movements examined with fMRI: effect of movement type and rate

Journal of neurophysiology, 1999

The human frontomesial cortex reportedly contains at least four cortical areas that are involved ... more The human frontomesial cortex reportedly contains at least four cortical areas that are involved in motor control: the anterior supplementary motor area (pre-SMA), the posterior SMA (SMA proper, or SMA), and, in the anterior cingulate cortex, the rostral cingulate zone (RCZ) and the caudal cingulate zone (CCZ). We used functional magnetic resonance imaging (fMRI) to examine the role of each of these mesial motor areas in self-initiated and visually triggered movements. Healthy subjects performed self-initiated movements of the right fingers (self-initiated task, SI). Each movement elicited a visual signal that was recorded. The recorded sequence of visual signals was played back, and the subjects moved the right fingers in response to each signal (visually triggered task, VT). There were two types of movements: repetitive (FIXED) or sequential (SEQUENCE), performed at two different rates: SLOW or FAST. The four regions of interest (pre-SMA, SMA, RCZ, CCZ) were traced on a high-resol...

Research paper thumbnail of Frontal and parietal networks for conditional motor learning: a positron emission tomography study

Journal of neurophysiology, 1997

Studies on nonhuman primates show that the premotor (PM) and prefrontal (PF) areas are necessary ... more Studies on nonhuman primates show that the premotor (PM) and prefrontal (PF) areas are necessary for the arbitrary mapping of a set of stimuli onto a set of responses. However, positron emission tomography (PET) measurements of regional cerebral blood flow (rCBF) in human subjects have failed to reveal the predicted rCBF changes during such behavior. We therefore studied rCBF while subjects learned two arbitrary mapping tasks. In the conditional motor task, visual stimuli instructed which of four directions to move a joystick (with the right, dominant hand). In the evaluation task, subjects moved the joystick in a predetermined direction to report whether an arrow pointed in the direction associated with a given stimulus. For both tasks there were three rules: for the nonspatial rule, the pattern within each stimulus determined the correct direction; for the spatial rule, the location of the stimulus did so; and for the fixed-response rule, movement direction was constant regardless...

Research paper thumbnail of Sequential mapping favours the hypothesis of distinct generators for Na and Pa middle latency auditory evoked potentials

Electroencephalography and clinical neurophysiology

The temporo-spatial organization of Na and Pa middle latency auditory components evoked by monaur... more The temporo-spatial organization of Na and Pa middle latency auditory components evoked by monaural clicks delivered separately to right and left ears was assessed by sequential mapping of scalp potentials. The potential field distribution was found to be different for the two components and was assessed by calculating the maximal potential differences in the Na/Pa time period. These data are compatible with the hypothesis that distinct generators are responsible for the two components. Scalp potential field configuration observed for Na suggests a deep generator, which could be situated at the mesencephalic or diencephalic level. Bilateral cortical generators tangentially orientated satisfactorily account for the distribution of the Pa potential field, which could be related to simultaneous activation of both supratemporal auditory cortices in response to monaural stimulation.

Research paper thumbnail of LP1: Aging effects on EEG alpha activity during internal and external motor sequence generation

Clinical Neurophysiology, 2014

Question: The creation of conscious and meaningful perceptions from sensory information should be... more Question: The creation of conscious and meaningful perceptions from sensory information should be fast and action-guiding. This requires fast integration of stimulus-driven activity with endogenous processes, such as prior experiences and intentions. A flexible mechanism may increase the impact of endogenous processes when the quality of the sensory information is poor or inconclusive. Visual illusions, such as visual ambiguity, provide a tool to investigate the brain response when the sensory information available is largely inconclusive for the generation of a meaningful percept. Methods: The EEG response during ambiguous and unambiguous perception was measured in twelve participants. Artefact-free epochs were extracted and the oscillatory theta response was extracted for all epochs using a single Morlet wavelet of six cycles and a centre frequency of 5.5 Hz (approximate frequency range: 4 to 7 Hz). Results: The EEG theta response was larger at frontal than at occipital regions in all of our twelve participants when the stimulus was ambiguous. This pattern was not found during unambiguous perception. Perceptual switches lead to an overall increase of theta activity. Conclusions: This outcome indicates that the contribution of endogenous processes on perception is variable. Anterior theta activity is specifically important for coherent perception when sensory information is ambiguous or inconclusive. Flexibility of endogenous processes may be a general phenomenon adjusting neural communication strategies on task demands (see also Mathes et al., 2012, Psychophysiology).

Research paper thumbnail of P395: Switching from bimanual to unimanual tapping reveals two distinct post-switching beta synchronization processes

Clinical Neurophysiology, 2014

Research paper thumbnail of Neural networks for braille reading by the blind include visual cortex

Research paper thumbnail of Decomposition and evaluation of activity in multiple event-related trials

IEEE 12th International Conference on BioInformatics and BioEngineering, BIBE 2012, 2012

ABSTRACT It is generally accepted that evoked and induced activations represent different aspects... more ABSTRACT It is generally accepted that evoked and induced activations represent different aspects of cerebral functions during an Event Related Potentials (ERP) experiment. Independent Component Analysis (ICA) has been successfully applied to event related electroencephalography (EEG) to decompose it into a sum of spatially fixed and temporally independent components that can be attributed to underlying cortical activity. A major problem in the application of ICA is the stability of estimated independent components. In this paper we exploited the split-half approach to assess component stability. We used different measures quantifying both phase and energy aspects of the ERP, in order to distinguish evoked from induced oscillations. We applied these measures to the stable independent components derived from a dataset of progressive Mild Cognitive Impairment (PMCI) and elderly controls. We found reduced energy in the induced theta activity in PMCI subjects, in accordance with previous studies. In addition, PMCI subjects presented lower phase-locking values and diminished late alpha band energy in contrast to controls.

Research paper thumbnail of The Color Center in the Cerebral-Cortex of Man

Research paper thumbnail of Working memory load-related electroencephalographic parameters can differentiate progressive from stable mild cognitive impairment

Neuroscience, 2007

Recent studies described several changes of endogenous event-related potentials (ERP) and brain r... more Recent studies described several changes of endogenous event-related potentials (ERP) and brain rhythm synchronization during memory activation in patients with Alzheimer's disease (AD). To examine whether memory-related EEG parameters may predict cognitive decline in mild cognitive impairment (MCI), we assessed P200 and N200 latencies as well as beta event-related synchronization (ERS) in 16 elderly controls (EC), 29 MCI cases and 10 patients with AD during the successful performance of a pure attentional detection task as compared with a highly working memory demanding two-back task. At 1 year follow-up, 16 MCI patients showed progressive cognitive decline (PMCI) and 13 remained stable (SMCI). Both P200 and N200 latencies in the two-back task were longer in PMCI and AD cases compared with EC and SMCI cases. During the interval 1000 ms to 1700 ms after stimulus, beta ERS at parietal electrodes was of lower amplitude in PMCI and AD compared with EC and SMCI cases. Univariate models showed that P200, N200 and log% beta values were significantly related to the SMCI/PMCI distinction with areas under the receiver operating characteristic curve of 0.93, 0.78 and 0.72, respectively. The combination of all three EEG hallmarks was the stronger predictor of MCI deterioration with 90% of correctly classified MCI cases. Our data reveal that PMCI and clinically overt AD share the same pattern of working memory-related EEG activation characterized by increased P200-N200 latencies and decreased beta ERS. They also show that P200 latency during the two-back task may be a simple and promising EEG marker of rapid cognitive decline in MCI.

Research paper thumbnail of A controlled positron emission tomography study of obsessive and neutral auditory stimulation in obsessive-compulsive disorder with checking rituals

Psychiatry Research, 1996

Research paper thumbnail of Electrical stimulation of precentral cortical area in the treatment of central pain: electrophysiological and PET study

Research paper thumbnail of Deficient activation of the motor cortical network in patients with writer's cramp

Neurology, 1999

... The decreased activation in sensorimotor cortex during the sustained contraction in writer&#x... more ... The decreased activation in sensorimotor cortex during the sustained contraction in writer's cramppatients is not ... detect functional relations between different brain structures in the absence of tangible activation.45 In writer's cramp patients, the reduced putaminal correlations ...

Research paper thumbnail of Changes of middle latency auditory evoked potentials during natural sleep in humans

Neurology, 1989

During natural nocturnal sleep, Na and Pa middle latency auditory evoked potentials (MLAEPs) unde... more During natural nocturnal sleep, Na and Pa middle latency auditory evoked potentials (MLAEPs) underwent significant variations which were related to sleep stages. The deepening of sleep from stage II to stage IV was paralleled by a latency shift and an amplitude decrease of Na and Pa, while MLAEPs were similar in wakefulness and REM sleep. Moreover, Na and Pa components tended to shift over the hemisphere contralateral to the stimulated ear during sleep. These findings demonstrate that the responsiveness of the auditory cortex to acoustic stimuli is modulated during sleep. Vigilance should be monitored during MLAEP recordings in patients.

Research paper thumbnail of Gender Difference in Premotor Activity during Active Tactile Discrimination

NeuroImage, 2000

To investigate possible gender differences in tactile discrimination tasks, we measured cerebral ... more To investigate possible gender differences in tactile discrimination tasks, we measured cerebral blood flow of seven men and seven women using positron emission tomography and (15)O water during tactile tasks performed with the right index finger. A nondiscrimination, somatosensory control task activated the left primary sensorimotor cortex and the left parietal operculum extending to the posterior insula without any gender difference. Compared with the control task, discrimination tasks activated the superior and inferior parietal lobules bilaterally, right dorsal premotor cortex, and dorsolateral prefrontal cortex in both genders, consistent with the notion of right hemisphere involvement during exploratory attentional movements. In both genders, symmetric activation of the superior and inferior parietal lobules and asymmetric activation of the right dorsolateral prefrontal cortex were confirmed. The former is consistent with the spatial representation of the tactile input and the latter with the spatial working memory. However, activation of the dorsal premotor cortex was asymmetric in men, whereas it was symmetric in women, the gender difference being statistically significant. This may suggest gender differences in motor programs for exploration in manipulospatial tasks such as tactile discrimination with active touch, possibly by greater interhemispheric interaction through the dorsal premotor cortices in women than in men.

Research paper thumbnail of Cerebral Processes Related to Visuomotor Imagery and Generation of Simple Finger Movements Studied with Positron Emission Tomography

Research paper thumbnail of Broca's area and mental preparation