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G Cadoret

Publications and source records attributed to G Cadoret.

10 recordsLinked to original sources
PubMed2001

Selective activation of the ventrolateral prefrontal cortex in the human brain during active retrieval processing.

The present study examined the role of the prefrontal cortex in retrieval processing using functional magnetic resonance imaging in human subjects. Ten healthy subjects were scanned while they performed a task that required retrieval of specific aspects of visual information. In order to examine brain activity specifically associated with retrieval, we designed a task that had retrieval and control conditions that were perfectly matched in terms of depth of encoding, decision making and postretrieval monitoring and differed only in terms of whether retrieval was required. In the retrieval condition, based on an instructional cue, the subjects had to retrieve either the particular stimulus that was previously presented or its location. In the control condition, the cue did not instruct retrieval but shared with the instructional cues the function of alerting the subjects of the impending test phase. The comparison of activity between the retrieval and control conditions demonstrated a significant and selective increase in activity related to retrieval processes within the ventrolateral prefrontal cortical region, more specifically within area 47/12. These activity increases were bilateral but stronger in the right hemisphere. The present study by strictly controlling the level of encoding, postretrieval monitoring, and decision making has demonstrated a specific increase in the ventrolateral prefrontal region that could be clearly related to active retrieval processing, i.e. the active selection of particular stored visual representations.

Adult↗
PubMed1997

Scopolamine increases prehensile force during object manipulation by reducing palmar sweating and decreasing skin friction.

The aim of this study was to determine whether relatively long-term changes in skin friction induced by a pharmacological blockade of sweat excretion would alter the grip forces applied to objects of a variety of different surface textures and frictions. Five men and three women were asked to lift the vertically mounted armature of a linear motor between the thumb and index finger and to hold it against an opposing force for 2 s. A 1.0-kHz tone indicated to the subject that the manipulandum had been correctly positioned between the upper and lower position limits. The linear motor generated a 2.5-N force tangential to the skin surface simulating an object weighing approximately 250 g. Three different polyamide plastic surfaces (either smooth or etched with 1.0 mm high Braille beads evenly spaced at 2- or 3-mm intervals) contacted the fingers in these experiments. Subjects lifted and held in a precision grip one of the three surfaces for blocks of ten consecutive trials, but the order of presentation of the three different textures was varied to offset the effect of expectancy. On a second block of ten trials the subjects were requested to release the object slowly to measure the ratio of the grip force normal to the grasped surface to the tangential load force at the moment of slip. This ratio or its inverse provided the coefficient of friction or the slip ratio for a particular subject and surface condition. Twelve hours prior to a second recording session all subjects placed transdermal patches of 1.5 mg scopolamine behind each ear to reduce palmar sweating by blocking the muscarinic receptors of exocrine sweat glands. The subjects were re-tested following procedures that were identical to the first session. Scopolamine significantly reduced the friction of the skin on the smooth and 2-mm beaded surfaces, but the friction of the 3-mm beaded texture was unaffected. Scopolamine also caused subjects to increase both the peak and static grip forces for all the textures including the 3-mm beaded surface, suggesting that for two of the three surfaces they were responding to the increased slipperiness of the skin due to reduced sweat production.

Adult↗
PubMed1997

Comparison of the neuronal activity in the SMA and the ventral cingulate cortex during prehension in the monkey.

Two monkeys were trained to use the thumb and forefinger to lift and hold an instrumented apparatus within a narrow position window for 1 s. The device was equipped to measure the position and the grip and lifting forces exerted by the animal. On blocks of trials the weight and surface texture could be varied or a force-pulse perturbation could be systematically delivered 750 ms after the object entered the window. If unopposed, the perturbation would displace the hand from the position window, and in preparation for this perturbation the monkeys either increased their grip force before the perturbation or raised the object higher within the position window. Two clearly separated clusters of cells in the medial wall of the frontal lobe were found to be active in relation to the task. One group of cells (n = 115) was located in the caudal and medial part of area 6, in the supplementary motor area (SMA), and the other (n = 92) was located in the ventral bank of the cingulate sulcus (CMAv), in area 23c. In each area, neurons were characterized by their sensorimotor features clearly related to the hand in addition to their modulated activity in the task. In the SMA, 71% (42 of 59) of the neurons tested for receptive fields responded to peripheral and mainly proprioceptive stimulation, and 71% of them (30 of 42) received inputs from the hand. In the CMAv, 77% (48 of 62) of the neurons responded to peripheral proprioceptive stimulation, and 77% (37 of 48) exhibited receptive fields originating from the hand. Intracortical microstimulation applied to 43 sites in the SMA evoked discrete hand movements at 12 loci, whereas in the CMAv hand movements were observed at 8 of 27 sites tested with an average threshold of > 15 microA. A strong similarity was observed between the SMA and CMAv neurons in their sensorimotor features as well as the modulation of their activity in relation to the prehension task. In both areas the activity was poorly related to grip force and significant correlation with peak grip force was observed for only 9 and 7% of the CMAv and SMA neurons, respectively. In the SMA only five cells exhibited increased activity before the perturbation and in the CMAv no changes in activity were found despite the presence of clear preparatory increases in grip force in anticipation of the perturbation. The perturbation evoked reflexlike excitation of 38% (25 of 65) of the neurons in the CMAv and 28% (20 of 71) of the cells in the SMA; these cells were similar in magnitude and latency (approximately 50 ms) in both areas. In both the SMA and CMAv, most of the neurons increased their firing rate < 200 ms before the grip force onset and the overlap in the distribution of neuronal response times suggests a parallel activation of the SMA and CMAv neurons during the prehension task.

Animals↗
PubMed1996

Friction, not texture, dictates grip forces used during object manipulation.

1. Three men and seven women, 25-40 yr of age, were asked to use the thumb and index fingers to grasp, lift, and hold the armature of a linear motor generating a 2.0-N opposing force (simulating an object weighing approximately 200 g) for 2 s. The surface in contact with the fingers was composed of smooth or polyamide plastic etched with 1.0-mm high Braille beads separated at 2.0- or 3.0-mm intervals measured from apex to apex. The surfaces were left either untreated or coated with talc, water, or sucrose films designed to change the coefficient of friction with the skin. Talc reduced the coefficient of friction, whereas water and sucrose both increased the friction against the skin. In all, 12 surface conditions were used to evaluate the effects of texture and friction on the grip force during lifting and holding. 2. For all subjects the inverse coefficient of friction was associated with proportionately scaled increases in grip force, regardless of surface texture. The peak lifting force as well as the static force used to hold the object stationary were significantly correlated with the inverse of the coefficient of friction. When coatings were applied to dissimilar surface textures to produce similar coefficients of friction, the grip force profiles were nearly identical. When strong adhesives increased the friction of the smooth surface compared with textured surfaces, grip forces decreased as friction increased. That is, although the untreated smooth surface had less friction than either of the two textured surfaces, the addition of sucrose increased the smooth surface friction to a higher level than either of the similarly treated textured surfaces. As a result, the effect of surface friction could be dissociated from the effect of either surface texture or coating. Friction appears to be a more important factor in determining the grip force than either texture or surface films at least for the range of textures and coatings examined in this study.

Adhesiveness↗
PubMed1995

EMG analysis of harmaline-induced tremor in normal and three strains of mutant mice with Purkinje cell degeneration and the role of the inferior olive.

1. The effects of intraperitoneal injections of 10 mg/kg harmaline were tested in normal mice and three strains of cerebellar mutant mice with Purkinje cell degeneration. Ten normal (wild-type) mice (+/+), as well as five lurcher (lc/+), six nervous (nr/nr), and eight Purkinje cell degeneration (pcd/pcd) mutants were implanted with chronic electromyogram (EMG) electrodes in the hamstring and quadriceps muscle groups of the right hindlimb. 2. EMGs were recorded in each of the mice during spontaneous activity before and after intraperitoneal injections of 0.3 ml harmaline (10 mg/kg). Spectral analysis was used to quantify the amplitude and frequency of tremor found in the EMGs after harmaline administration. Normal mice responded to harmaline with strong, continuous 11- to 14-Hz tremor. Mutants from the pcd/pcd strain also reacted with continuous tremor, but of lower amplitude and frequency. In contrast, nr/nr mutants exhibited intermittent paroxysmal tremor lasting for only a few seconds, and lc/+ mutants showed no evidence of tremor whatsoever. 3. In order to detect covert tremor that was possibly not revealed by focal intramuscular EMG recordings, several mutant and normal mice were also tested on a suspended platform to which an accelerometer was attached. The results confirmed the findings from EMG recordings. 4. An incidental observation made during the course of this study was that harmaline tremor disappeared from the normal mouse during swimming and reappeared when the animal was withdrawn from the water. 5. Although Purkinje cells appeared to increase both the depth of modulation and the frequency of tremor, the inhibitory action of the cerebellar cortex does not seem to be essential for the generation of tremor. 6. Parasagittal cerebellar sections of the normal, wild-type mice and the three strains of cerebellar mutant mice of various ages were stained with cresyl violet and examined for Purkinje cell degeneration. Purkinje cell degeneration was found to be complete in the pcd/pcd and lc/+ strains. Although an initial examination of parasagittal sections of the nr/nr strain failed to find any surviving Purkinje cells, further examination of sections cut in the coronal plane revealed small clusters of Purkinje cells in the vermal area of the posterior lobe. 7. The retrograde transport of wheat-germ-agglutinin-conjugated horseradish peroxidase (WGA-HRP) pressure-injected into the cerebellar cortex was used to study the olivocerebellar projections in the wild-type mice and the three strains of cerebellar mutant mice.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Input-output properties of hand-related cells in the ventral cingulate cortex in the monkey.

1. Neurons with proprioceptive or cutaneous receptive fields associated with the hand were identified in the ventral bank of the cingulate sulcus in the monkey. Cells with proprioceptive fields outnumbered cells receiving cutaneous afferents by more than three to one. No cells were encountered that received convergent proprioceptive and cutaneous input. The high concentration of these neurons in the lateral depth of the cingulate sulcus establishes that a distinct hand representation exists within the rostral part of area 23c. 2. Hand-related neurons in area 23c exhibited strong activity modulations during grasping, lifting, and holding an object with the contralateral thumb and index finger. Force pulse perturbations applied to the object elicited excitatory responses at latencies of approximately 45 ms. The modulation of the cellular activity and the input-output properties of these cingulate neurons suggest that, like neurons of primary motor and sensory cortex, these cingulate neurons are also involved in the sensorimotor control of finger movements.

Afferent Pathways↗
PubMed1994

Early development of reaching in Down syndrome infants.

The development of reaching was studied in 10 Down syndrome and 10 control infants. Arm movements were recorded at 5, 7 and 9 months for the control group and 7, 9 and 11 months for the group with Down syndrome. Arm movements were recorded using a 3-dimensional video-motion analysis system. In both groups, there was a change from bilateral to unilateral responses with age, although Down syndrome infants used bilateral responses longer. Arm velocity increased significantly with age in the control group, but not in the Down syndrome group. Several characteristics of the reaching movements were clearly different between the Down syndrome and control groups. The deviations from a straight line and the changes in the plane of motion suggest that Down syndrome infants have more difficulty in controlling their arm movements. As expected, the results indicate the presence of a delay in the development of reaching in Down syndrome infants. They also suggest the presence of a deficit in the organization of their reaching movement.

Aging↗