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Biomedical subjects

Pietro Mazzoni

Publications and source records attributed to Pietro Mazzoni.

6 recordsLinked to original sources
PubMed2006

Cross-fixation transfer of motion aftereffects with expansion motion.

It has been shown that motion aftereffect (MAE) not only is present at the adapted location but also partially transfers to nearby non-adapted locations. However, it is not clear whether MAE transfers across the fixation point. Since cells in area MSTd have receptive fields that cover both sides of the fixation point and since many MSTd cells, but not cells in earlier visual areas, prefer complex motion patterns such as expansion, we tested cross-fixation transfer of MAE induced by expanding random-dots stimuli. We also used rightward translational motion for comparison. Subjects adapted to motion patterns on a fixed side of the fixation point. Dynamic MAE was then measured with a nulling procedure at both the adapted site and the mirror site across the fixation point. Subjects' eye fixation during stimulus presentation was monitored with an infrared eye tracker. At the adapted site, both the expansion and the translation patterns generated strong MAEs, as expected. However, only the expansion pattern, but not translation pattern, generated significant MAE at the mirror site. This remained true even after we adjusted stimulus parameters to equate the strengths of the expansion MAE and translation MAE at the adapted site. We conclude that there is cross-fixation transfer of MAE for expansion motion but not for translational motion.

Figural Aftereffect↗
PubMed2006

An implicit plan overrides an explicit strategy during visuomotor adaptation.

The relationship between implicit and explicit processes during motor learning, and for visuomotor adaptation in particular, is poorly understood. We set up a conflict between implicit and explicit processes by instructing subjects to counter a visuomotor rotation using a cognitive strategy in a pointing task. Specifically, they were told the exact nature of the directional perturbation, a rotation that directed them 45 degrees counterclockwise from the desired target, and they were instructed to counter it by aiming for the neighboring clockwise target, 45 degrees away. Subjects were initially successful in completely negating the rotation with this strategy. Surprisingly, however, they were unable to sustain explicit control and made increasingly large errors to the desired target. The cognitive strategy failed because subjects simultaneously adapted unconsciously to the rotation to the neighboring target. Notably, the rate of implicit adaptation to the neighboring target was not significantly different from rotation adaptation in the absence of an opposing explicit strategy. These results indicate that explicit strategies cannot substitute for implicit adaptation to a visuomotor rotation and are in fact overridden by the motor planning system. This suggests that the motor system requires that planned and executed trajectories remain congruous in visual space, and enforces this correspondence even at the expense of an opposing explicit task goal.

Adaptation, Physiological↗
PubMed2006

Generalization of motor learning depends on the history of prior action.

Generalization of motor learning refers to our ability to apply what has been learned in one context to other contexts. When generalization is beneficial, it is termed transfer, and when it is detrimental, it is termed interference. Insight into the mechanism of generalization may be acquired from understanding why training transfers in some contexts but not others. However, identifying relevant contextual cues has proven surprisingly difficult, perhaps because the search has mainly been for cues that are explicit. We hypothesized instead that a relevant contextual cue is an implicit memory of action with a particular body part. To test this hypothesis we considered a task in which participants learned to control motion of a cursor under visuomotor rotation in two contexts: by moving their hand through motion of their shoulder and elbow, or through motion of their wrist. Use of these contextual cues led to three observations: First, in naive participants, learning in the wrist context was much faster than in the arm context. Second, generalization was asymmetric so that arm training benefited subsequent wrist training, but not vice versa. Third, in people who had prior wrist training, generalization from the arm to the wrist was blocked. That is, prior wrist training appeared to prevent both the interference and transfer that subsequent arm training should have caused. To explain the data, we posited that the learner collected statistics of contextual history: all upper arm movements also move the hand, but occasionally we move our hands without moving the upper arm. In a Bayesian framework, history of limb segment use strongly affects parameter uncertainty, which is a measure of the covariance of the contextual cues. This simple Bayesian prior dictated a generalization pattern that largely reproduced all three findings. For motor learning, generalization depends on context, which is determined by the statistics of how we have previously used the various parts of our limbs.

Adult↗
PubMed2003

Huntington's disease.

In this case study, we describe the symptoms, neurological exam, neuropsychological test results, and brain pathology of a man who died with Huntington's disease (HD). HD is a rare neurodegenerative disease. Like other movement disorders involving the basal ganglia, HD affects motor, cognitive, and psychiatric functioning. The disease follows an autosomal dominant pattern of inheritance, with onset of symptoms most commonly occurring in the late 30s or early 40s, as in this patient. HD is caused by an unstable expansion of the trinucleotide CAG, coding for glutamine, on chromosome 4. Despite knowledge of the gene mutation responsible for HD, no definitive treatment is currently available to slow or halt progression of the disease. However, symptomatic treatment can significantly improve the quality of life for patients with HD.

Fatal Outcome↗