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Biomedical subjects

Daniel Z Press

Publications and source records attributed to Daniel Z Press.

11 recordsLinked to original sources
PubMed2006

Disruption of primary motor cortex before learning impairs memory of movement dynamics.

Although multiple lines of evidence implicate the primary motor cortex (M1) in motor learning, the precise role of M1 in the adaptation to novel movement dynamics and in the subsequent consolidation of a memory of those dynamics remains unclear. Here we used repetitive transcranial magnetic stimulation (rTMS) to dissociate the contribution of M1 to these distinct aspects of motor learning. Subjects performed reaching movements in velocity-dependent force fields over three epochs: a null-field baseline epoch, a clockwise-field learning epoch (15 min after the baseline epoch), and a clockwise-field retest epoch (24 h after the learning epoch). Half of the subjects received 15 min of 1 Hz rTMS to M1 between the baseline and learning epochs. Subjects given rTMS performed identically to control subjects during the learning epoch. However, control subjects performed with significantly less error than rTMS subjects in the retest epoch on the following day. These results suggest that M1 is not critical to the network supporting motor adaptation per se but that, within this network, M1 may be important for initiating the development of long-term motor memories.

Adaptation, Physiological↗
PubMed2006

Intermittent practice facilitates stable motor memories.

Humans adaptively control reaching movements to maintain good performance in the presence of novel forces acting on the arm. A recent study suggested that motor memories of different force conditions are not transformed from fragile to stable states, but rather are always vulnerable to interference from newly learned conditions (Caithness et al., 2004). This is contrary to the results of previous studies (Brashers-Krug et al., 1996; Shadmehr and Brashers-Krug, 1997), although all of these studies followed similar methods. Here, we show that a seemingly insignificant and inconsistently applied methodological detail may reconcile this discrepancy. Catch trials, in which the novel forces are removed, may be randomly interspersed among the more frequent force trials to assess how a subject is learning to predict the pattern of forces. In the absence of an interfering condition, subjects retained their learning until retest a day later regardless of whether they experienced catch trials. But in the presence of an interfering condition, only the subjects who had experienced forces intermittently retained their learning and thereby showed resistance to the interference. Thus, intermittent rather than constant practice conditions appear to be critical for dynamic motor memory stabilization.

Adaptation, Physiological↗
PubMed2005

The contribution of sleep to improvements in working memory scanning speed: a study of prolonged sleep restriction.

Working memory scanning and motor response speeds were assessed in chronically sleep restricted participants using the Sternberg item recognition paradigm (SIRP). Twenty-two healthy volunteers (ages 21-30) living in a controlled hospital environment were allowed either 4h of sleep opportunity (50% of habitual sleep) or 8h of sleep opportunity (100% of habitual sleep) for 12 days. Working memory scanning efficiency (time taken to access an item in working memory) was tested for the first 9 days of sleep restriction and improved over time in participants permitted an 8h sleep period, but did not change significantly in participants permitted a 4h sleep period. Speed of motor response (reaction time independent of cognitive processing) did not change significantly in either group. These results indicate that the efficiency of working memory scanning can improve with repeated practice given sufficient sleep, and that prolonged sleep restriction to 50% of habitual sleep prevents this improvement.

Adult↗
PubMed2005

Off-line learning of motor skill memory: a double dissociation of goal and movement.

Acquiring a new skill requires learning multiple aspects of a task simultaneously. For example, learning a piano sonata requires learning the musical notes and being able to implement this goal by learning the appropriate sequence of finger movements. After practice, skill continues to develop off-line during a period of consolidation. Here we show that different aspects of a procedural memory are processed separately during consolidation: Only the movement sequence is enhanced over the day; whereas only the goal is enhanced over a night of sleep. This double dissociation suggests that distinct systems, enhancing different aspects of a procedural memory, support improvements during consolidation. Consolidation is not a single process; instead, there are multiple routes to off-line learning, and the engagement of these distinct mechanisms is determined by when consolidation takes place.

Adult↗
PubMed2005

Off-line learning and the primary motor cortex.

We are all familiar with acquiring skills during practice, but skill can also continue to develop between practice sessions. These "off-line" improvements are frequently supported by sleep, but they can be time dependent when a skill is acquired unintentionally. The magnitude of these over-day and overnight improvements is similar, suggesting that a similar mechanism may support both types of off-line improvements. However, here we show that disruption of the primary motor cortex with repetitive transcranial magnetic stimulation blocks off-line improvements over the day but not overnight. This suggests that a memory may be rescued overnight and subsequently enhanced or that different aspects of a skill, with differential dependencies on the primary motor cortex, are enhanced over day and overnight. Off-line improvements of similar magnitude are not supported by similar mechanisms; instead, the mechanisms engaged may depend on brain state.

Adult↗
PubMed2005

The time course of off-line motor sequence learning.

The acquisition of motor skill occurs with practice, but skill can also increase between sessions, a process termed "off-line learning". Here, we investigated the amount of time required for the off-line development of skills. Participants were tested on an implicit version of the Serial Reaction Time Task and re-tested 1, 4 or 12 h later. Only those re-tested 4 h or 12 h after initial testing showed off-line improvements. This demonstrates that implicitly acquired skills can increase between sessions and the process occurs over hours.

Adolescent↗
PubMed2004

Awareness modifies the skill-learning benefits of sleep.

Behind every skilled movement lies months of practice. However, practice alone is not responsible for the acquisition of all skill; performance can improve between, not just within, practice sessions. An important principle shaping these offline improvements may be an individual's awareness of learning a new skill. New skills, such as a sequence of finger movements, can be learned unintentionally (with little awareness for the sequence, implicit learning) or intentionally (explicit learning). We measured skill in an implicit and explicit sequence-learning task before and after a 12 hr interval. This interval either did (8 p.m. to 8 a.m.) or did not (8 a.m. to 8 p.m.) include a period of sleep. Following explicit sequence learning, offline skill improvements were only observed when the 12 hr interval included sleep. This overnight improvement was correlated with the amount of NREM sleep. The same improvement could also be observed in the evening (with an interval from 8 p.m. to 8 p.m.), so it was not coupled to retesting at a particular time of day and cannot therefore be attributed to circadian factors. In contrast, in the implicit learning task, offline learning was observed regardless of whether the 12 hr interval did or did not contain a period of sleep. However, these improvements were not observed with only a 15 min interval between sessions. Therefore, the practice available within each session cannot account for these skill improvements. Instead, sufficient time is necessary for offline learning to occur. These results show a behavioral dissociation, based upon an individual's awareness for having learned a sequence of finger movements. Offline learning is sleep dependent for explicit skills but time dependent for implicit skills.

Awareness↗
PubMed2004

Perceptual functions in prosopagnosia.

Some patients with prosopagnosia may have an apperceptive basis to their recognition defect. Perceptual abnormalities have been reported in single cases or small series, but the causal link of such deficits to prosopagnosia is unclear. Our goal was to identify candidate perceptual processes that might contribute to prosopagnosia, by subjecting several prosopagnosic patients to a battery of functions that may be necessary for accurate facial perception. We tested seven prosopagnosic patients. Three had unilateral right occipitotemporal lesions, two had bilateral posterior occipitotemporal lesions, and one had right anterior-to-occipital temporal damage along with a small left temporal lesion. These lesions all included the fusiform face area, in contrast to one patient with bilateral anterior temporal lesions. Most patients had impaired performance on face-matching tests and difficulty with subcategory judgments for non-face objects. The most consistent deficits in patients with lesions involving the fusiform face area were impaired perception of spatial relations in dot patterns and reduced contrast sensitivity in the 4 to 8 cycles deg(-1) range. Patients with bilateral lesions were impaired in saturation discrimination. Luminance discrimination was normal in all but two patients, and spatial resolution was uniformly spared. Curvature and line-orientation discrimination were impaired in only one patient, who also had the most difficulty with more basic-level object recognition. We conclude that deficits in luminance, spatial resolution, curvature, line orientation, and contrast at low spatial frequencies are unlikely to contribute to apperceptive prosopagnosia. More relevant may be contrast sensitivity at higher spatial frequencies and the analysis of object spatial structure. Deficits in these functions may impair perception of subtle variations in object shape, and may be one mechanism by which the recognition defect in prosopagnosia can extend to other classes of object subcategorization.

Adult↗
PubMed2003

Developmental prosopagnosia: a study of three patients.

We studied perception in three patients with prosopagnosia of childhood onset. All had trouble with other 'within-category' judgments. All were deficient on face matching tests and severely impaired on tests of perception of the spatial relations of facial features and abstract designs, indicating a deficit in the encoding of coordinate relationships, similar to adult-onset prosopagnosia with lesions of the fusiform face area. Two had difficulty perceiving feature colour, which correlated with reduced luminance sensitivity. In contrast to adult-onset patients, saturation discrimination was spared in two and spatial resolution impaired in two. Curvature discrimination was relatively spared. Contrast sensitivity showed variable reductions at different spatial frequencies. We conclude that developmental prosopagnosia is similar to the adult-onset form in encoding deficits for the spatial arrangement of facial elements. Deficits in luminance perception and spatial resolution are more associated with defective encoding for basic object-level recognition, as shown on tests of object and spatial perception.

Adult↗
PubMed2002

Lesions of the fusiform face area impair perception of facial configuration in prosopagnosia.

BACKGROUND: Prosopagnosia, the inability to recognize faces, is associated with medial occipitotemporal lesions, especially on the right. Functional imaging has revealed a focal region in the right fusiform gyrus activated specifically during face perception. OBJECTIVE: The study attempted to determine whether lesions of this region were associated with defects in face perception in patients with prosopagnosia. METHODS: Five patients with acquired prosopagnosia were tested. They were asked to discriminate faces in which the spatial configuration of features had been altered. This was contrasted with their discrimination of changes in feature color, an alteration that does not affect spatial relations. RESULTS: All four patients whose lesions included the right fusiform face area were severely impaired in discriminating changes in the spatial position of features. The one patient with anterior bilateral lesions was normal in this perceptual ability. For three of the five patients, accuracy was normal for changes in eye color. When subjects knew that only changes in mouth position would be shown, performance improved markedly in two of the four patients who were impaired in the initial test. CONCLUSION: Perception of facial configuration is impaired in patients with prosopagnosia whose lesions involve the right fusiform gyrus. This deficit is especially manifest when attention must be distributed across numerous facial elements. It does not occur with more anterior bilateral temporal lesions. Loss of this ability may contribute to the recognition defect in some forms of prosopagnosia.

Adult↗