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Gianfranco Bosco

Publications and source records attributed to Gianfranco Bosco.

8 recordsLinked to original sources
PubMed2005

Representation of visual gravitational motion in the human vestibular cortex.

How do we perceive the visual motion of objects that are accelerated by gravity? We propose that, because vision is poorly sensitive to accelerations, an internal model that calculates the effects of gravity is derived from graviceptive information, is stored in the vestibular cortex, and is activated by visual motion that appears to be coherent with natural gravity. The acceleration of visual targets was manipulated while brain activity was measured using functional magnetic resonance imaging. In agreement with the internal model hypothesis, we found that the vestibular network was selectively engaged when acceleration was consistent with natural gravity. These findings demonstrate that predictive mechanisms of physical laws of motion are represented in the human brain.

Acceleration↗
PubMed2004

Fast adaptation of the internal model of gravity for manual interceptions: evidence for event-dependent learning.

We studied how subjects learn to deal with two conflicting sensory environments as a function of the probability of each environment and the temporal distance between repeated events. Subjects were asked to intercept a visual target moving downward on a screen with randomized laws of motion. We compared five protocols that differed in the probability of constant speed (0g) targets and accelerated (1g) targets. Probability ranged from 9 to 100%, and the time interval between consecutive repetitions of the same target ranged from about 1 to 20 min. We found that subjects systematically timed their responses consistent with the assumption of gravity effects, for both 1 and 0g trials. With training, subjects rapidly adapted to 0g targets by shifting the time of motor activation. Surprisingly, the adaptation rate was independent of both the probability of 0g targets and their temporal distance. Very few 0g trials sporadically interspersed as catch trials during immersive practice with 1g trials were sufficient for learning and consolidation in long-term memory, as verified by retesting after 24 h. We argue that the memory store for adapted states of the internal gravity model is triggered by individual events and can be sustained for prolonged periods of time separating sporadic repetitions. This form of event-related learning could depend on multiple-stage memory, with exponential rise and decay in the initial stages followed by a sample-and-hold module.

Adaptation, Physiological↗
PubMed2004

Cerebellar encoding of limb position.

In this paper, we review single and multijoint studies that, over the years, have provided insight on the cerebellar encoding of limb spatial position. In particular, we present support to the idea that the cerebellum integrates signals from multiple sources to encode global limb parameters. Then, we highlight the result of recent studies that analyzed quantitatively the relationships between limb end-point position and cerebellar activity. These findings suggest that the cerebellum may share with other central sensory-motor structures an anisotropic representation of limb position characterized by a strong bias along the anteroposterior axis. Finally, we speculate that this anisotropy may also subtend an internal representation of limb mechanics.

Animals↗
PubMed2003

Internal models of target motion: expected dynamics overrides measured kinematics in timing manual interceptions.

Prevailing views on how we time the interception of a moving object assume that the visual inputs are informationally sufficient to estimate the time-to-contact from the object's kinematics. Here we present evidence in favor of a different view: the brain makes the best estimate about target motion based on measured kinematics and an a priori guess about the causes of motion. According to this theory, a predictive model is used to extrapolate time-to-contact from expected dynamics (kinetics). We projected a virtual target moving vertically downward on a wide screen with different randomized laws of motion. In the first series of experiments, subjects were asked to intercept this target by punching a real ball that fell hidden behind the screen and arrived in synchrony with the visual target. Subjects systematically timed their motor responses consistent with the assumption of gravity effects on an object's mass, even when the visual target did not accelerate. With training, the gravity model was not switched off but adapted to nonaccelerating targets by shifting the time of motor activation. In the second series of experiments, there was no real ball falling behind the screen. Instead the subjects were required to intercept the visual target by clicking a mousebutton. In this case, subjects timed their responses consistent with the assumption of uniform motion in the absence of forces, even when the target actually accelerated. Overall, the results are in accord with the theory that motor responses evoked by visual kinematics are modulated by a prior of the target dynamics. The prior appears surprisingly resistant to modifications based on performance errors.

Acceleration↗
PubMed2003

Anisotropic representation of forelimb position in the cerebellar cortex and nucleus interpositus of the rat.

The relationship between the spatial location of limb and the activity of cerebellar neurons has received little attention and its nature still remains ambiguous. To address this question we studied the activity of Purkinje and nucleus interpositus cells in relation to the spatial location of rat forelimb. A computer-controlled robot arm displaced the limb passively across 15 positions distributed on a parasagittal plane. The limb was upheld for 8 s in each position, which was identified by the Cartesian coordinates of the forepaw. We selected the neurons whose activities were significantly modulated by forepaw position and found that the majority represented preferentially one spatial dimension of the Cartesian plane both in the cerebellar cortex and nucleus interpositus. In particular, the antero-posterior axis was best represented in cerebellar neuronal discharges. This result suggests that the intermediate part of the cerebellum might encode limb position by way of an anisotropic representation of the spatial coordinates of the limb end-point.

Action Potentials↗
PubMed2003

Sophisticated spinal contributions to motor control.

The neural circuitry of the spinal cord is capable of solving some of the most complex problems in motor control. Therefore, spinal mechanisms are much more sophisticated than many neuroscientists give them credit for. A key issue in motor control is how sensory inputs direct and inform motor output,--that is, the sensorimotor process. Other major issues involve the actual control of the motor apparatus. In general, there are at least three basic requirements for motor control: the transformations that map information from sensory to motor coordinates, the specification of individual muscle activations to achieve a kinematic goal, and the control of multiple degrees of freedom. Here, we make the case that the vertebrate spinal cord has the capacity to solve each of these problems to a degree that is relevant for normal behavior.

Animals↗
PubMed2002

Kinematic features of passive forelimb movements and rat cuneate neuron discharges.

We examined the role of main and external cuneate nuclei neurons in processing sensory information during forelimb passive movement. We recorded activity of neurons using circular and figure-eight trajectories, at different speeds, in anaesthetized rats. A multivariate regression analysis was performed to correlate neural discharge to movement direction and speed, the two components of the velocity vector. We found that the activity of the majority of cuneate neurons related to passive movement velocity and that the directional component of the velocity vector accounted for a larger fraction of the variability in the firing rate than the scalar component (speed). These results indicate that cuneate cells can process whole limb afferent information to elaborate a representation of the movement velocity vector.

Algorithms↗