Biomedical subjects
Publications and source records attributed to Edwin M Robertson.
It is often assumed that the human brain only becomes active to support overt behaviour. A new study challenges this concept by showing that multiple neural circuits are engaged even at rest. We highlight two complementary hypotheses which seek to explain the function of this resting activity.
Skill improvements may develop between practice sessions during memory consolidation. Skill enhancement within an egocentric coordinate frame develops over wake, whereas skill enhancement in an allocentric coordinate frame develops over a night of sleep. We tested whether both types of improvement could develop over two different 24-h intervals: 8 am to 8 am or from 8 pm to 8 pm. We found that for each 24 h interval, only one type of skill improvement was seen. Despite passing through wake and a night of sleep participants only showed skill improvements commensurate with either a night of sleep or a day awake. The nature of the off-line skill enhancement was determined by when consolidation occurred within the normal sleep-wake cycle. We conclude that motor sequence consolidation is constrained either by having critical time windows or by a competitive interaction in which improvements within one co-ordinate frame actively block improvements from developing in the alternative co-ordinate frame.
Following its encoding, a memory undergoes consolidation. It may be possible to deepen our understanding of the mechanisms supporting consolidation by considering the complex architecture of a memory. Any behavior can be split into multiple components. For example, when learning a new skill we simultaneously learn the movement and the goal of that movement. Each of these components has a distinct representation within a memory. The "off-line" processing of each component may follow different rules, providing an explanation for the variety of performance changes supported by consolidation. By viewing a memory as a representation with multiple components, it is possible to bridge the gap between the behavioral changes, which define consolidation, and the biological mechanisms that support those changes. This is partly because different memory components can be mapped onto different neural circuits. With an increased understanding of consolidation, it may become possible to modulate these off-line processes to improve psychiatric and neurological rehabilitation.
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.
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.
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.
OBJECTIVE: To study the effects of depression and treatment with repetitive transcranial magnetic stimulation (rTMS) on sequence learning. BACKGROUND: Prefrontal dysfunction in depression may affect sequence learning and be amenable to normalization by rTMS. METHOD: The serial reaction time test (SRTT) was administered to 19 patients with major depressive disorder (MDD) and 20 nondepressed control participants. MDD patients were examined before and following treatment with rTMS to the left dorsolateral prefrontal cortex in daily sessions of 1600 stimuli at 10 Hz and at an intensity of 110% of the motor threshold. Treatment occurred over a 2-week interval of time. RESULTS: MDD and nondepressed groups differed significantly with respect to baseline response speed. Following treatment with rTMS, MDD participants demonstrated significantly improved mood, improved response speed, and improved procedural learning. CONCLUSIONS: Findings suggest that rTMS over a 2-week period improves performance on tasks of response speed and procedural memory in patients with MDD. These cognitive effects are greater in those patients who showed a significant antidepressant effect to rTMS intervention.
Information acquired during skill learning continues to be processed long after practice has ceased. An important aspect of this processing is thought to be the transformation of a memory from a fragile to a stable state: a concept challenged by a recent study.
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.
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