Is neuroenhancement by noninvasive brain stimulation a net zero-sum proposition?

In the past several years, the number of studies investigating enhancement of cognitive functions through noninvasive brain stimulation (NBS) has increased considerably. NBS techniques, such as transcranial magnetic stimulation and transcranial current stimulation, seem capable of enhancing cognitive functions in patients and in healthy humans, particularly when combined with other interventions, including pharmacologic, behavioral and cognitive therapies. The "net zero-sum model", based on the assumption that brain resources are subjected to the physical principle of conservation of energy, is one of the theoretical frameworks proposed to account for such enhancement of function and its potential cost. We argue that to guide future neuroenhancement studies, the net-zero sum concept is helpful, but only if its limits are tightly defined.

New insights in human memory interference and consolidation

Learning new facts and skills in succession can be frustrating because no sooner has new knowledge been acquired than its retention is being jeopardized by learning another set of skills or facts. Interference between memories has recently provided important new insights into the neural and psychological systems responsible for memory processing. For example, interference not only occurs between the same types of memories, but can also occur between different types of memories, which has important implications for our understanding of memory organization. Converging evidence has begun to reveal that the brain produces interference independently from other aspects of memory processing, which suggests that interference may have an important but previously overlooked function. A memory's initial susceptibility to interference and subsequent resistance to interference after its acquisition has revealed that memories continue to be processed 'off-line' during consolidation. Recent work has demonstrated that off-line processing is not limited to just the stabilization of a memory, which was once the defining characteristic of consolidation; instead, off-line processing can have a rich diversity of effects, from enhancing performance to making hidden rules explicit. Off-line processing also occurs after memory retrieval when memories are destabilized and then subsequently restabalized during reconsolidation. Studies are beginning to reveal the function of reconsolidation, its mechanistic relationship to consolidation and its potential as a therapeutic target for the modification of memories.

Resting state networks and memory consolidation

Despite their name, resting state networks (RSNs) provide a clear indication that the human brain may be hard-working. Unlike the cardiac and respiratory systems, which greatly reduce their rate of function during periods of inactivity, the human brain may have additional responsibilities during rest. One particularly intriguing function performed by the resting brain is the consolidation of recent learned information, which is known to take place over a period of several hours after learning. We recently reported that resting state brain activity is modulated by recent learning. We measured the brain activity using functional MRI during periods of rest that preceded and followed learning of a sensorimotor task, and found a network of brain areas that changed their resting activity. These areas are known to be involved in the acquisition and memory of such sensorimotor tasks. Furthermore, the changes were specific to a task that required learning, and were not found after motor performance without learning. Here we discuss the implications and possible extensions of this work and its relevance to the study of memory consolidation.

A distraction can impair or enhance motor performance

Humans have a prodigious capacity to perform multiple tasks simultaneously. Being distracted while, for example, performing a complex motor skill adds complexity to a task and thus leads to a performance impairment. Yet, it may not be just the presence or absence of a distraction that affects motor performance. Instead, the characteristics of the distraction may play a critical role in affecting human motor performance. Here, we show that performance of a motor sequence can be substantially enhanced by simultaneously learning an independent color sequence. In contrast, performance of the same motor sequence was impaired by concurrently counting the number of red cues that were in the color sequence. The color and motor sequences had different lengths (10 vs 12 items), different numbers of elements (five vs four elements), and different temporal patterns (randomly intermittent vs continuous) and thus were independent of one another. These observations show that distracting information does not always impair motor performance, and so is not a sufficient explanation for the impaired performance. Instead, the influence that a distraction exerts upon performance is mediated by the type of processes engaged: when similar core processes are engaged, motor performance is enhanced, whereas when very different processes are engaged (i.e., counting and sequence performance), performance is impaired. Thus, these observations deepen our understanding of how a distraction, depending on its characteristics, can either impair or enhance performance and may offer novel approaches to optimizing human cognition.

Sequence skill acquisition and off-line learning in normal aging

It is well known that certain cognitive abilities decline with age. The ability to form certain new declarative memories, particularly memories for facts and events, has been widely shown to decline with advancing age. In contrast, the effects of aging on the ability to form new procedural memories such as skills are less well known, though it appears that older adults are able to acquire some new procedural skills over practice. The current study examines the effects of normal aging on procedural memory more closely by comparing the effects of aging on the encoding or acquisition stage of procedural learning versus its effects on the consolidation, or between-session stage of procedural learning. Twelve older and 14 young participants completed a sequence-learning task (the Serial Reaction Time Task) over a practice session and at a re-test session 24 hours later. Older participants actually demonstrated more sequence skill during acquisition than the young. However, older participants failed to show skill improvement at re-test as the young participants did. Age thus appears to have a differential effect upon procedural learning stages such that older adults' skill acquisition remains relatively intact, in some cases even superior, compared to that of young adults, while their skill consolidation may be poorer than that of young adults. Although the effect of normal aging on procedural consolidation remains unclear, aging may actually enhance skill acquisition on some procedural tasks.

The resting human brain and motor learning

Functionally related brain networks are engaged even in the absence of an overt behavior. The role of this resting state activity, evident as low-frequency fluctuations of BOLD (see [1] for review, [2-4]) or electrical [5, 6] signals, is unclear. Two major proposals are that resting state activity supports introspective thought or supports responses to future events [7]. An alternative perspective is that the resting brain actively and selectively processes previous experiences [8]. Here we show that motor learning can modulate subsequent activity within resting networks. BOLD signal was recorded during rest periods before and after an 11 min visuomotor training session. Motor learning but not motor performance modulated a fronto-parietal resting state network (RSN). Along with the fronto-parietal network, a cerebellar network not previously reported as an RSN was also specifically altered by learning. Both of these networks are engaged during learning of similar visuomotor tasks [9-22]. Thus, we provide the first description of the modulation of specific RSNs by prior learning--but not by prior performance--revealing a novel connection between the neuroplastic mechanisms of learning and resting state activity. Our approach may provide a powerful tool for exploration of the systems involved in memory consolidation.

From creation to consolidation: a novel framework for memory processing

Long after playing squash, your brain continues to process the events that occurred during the game, thereby improving your game, and more generally, enhancing adaptive behavior. Understanding these mysterious processes may require novel theories.

Off-line processing: reciprocal interactions between declarative and procedural memories

The acquisition of declarative (i.e., facts) and procedural (i.e., skills) memories may be supported by independent systems. This same organization may exist, after memory acquisition, when memories are processed off-line during consolidation. Alternatively, memory consolidation may be supported by interactive systems. This latter interactive organization predicts interference between declarative and procedural memories. Here, we show that procedural consolidation, expressed as an off-line motor skill improvement, can be blocked by declarative learning over wake, but not over a night of sleep. The extent of the blockade on procedural consolidation was correlated to participants' declarative word recall. Similarly, in another experiment, the reciprocal relationship was found: declarative consolidation was blocked by procedural learning over wake, but not over a night of sleep. The decrease in declarative recall was correlated to participants' procedural learning. These results challenge the concept of fixed independent memory systems; instead, they suggest a dynamic relationship, modulated by when consolidation takes place, allowing at times for a reciprocal interaction between memory systems.

Inducing motor skill improvements with a declarative task

During sequence learning, individuals show motor-skill acquisition and an ability to verbally describe items within the sequence. We disrupted this latter, declarative component by having participants learn a word list immediately after sequence learning. This induced off-line skill improvements. We conclude that off-line memory processing relies not only on the engagement of neuroplastic mechanisms but also on the disengagement of an interaction between declarative and procedural memory systems.

Functional imaging: is the resting brain resting?

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.

Motor sequence consolidation: constrained by critical time windows or competing components

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.

Measuring safety climate in health care

AIM

To review quantitative studies of safety climate in health care to examine the psychometric properties of the questionnaires designed to measure this construct.

METHOD

A systematic literature review was undertaken to study sample and questionnaire design characteristics (source, no of items, scale type), construct validity (content validity, factor structure and internal reliability, concurrent validity), within group agreement, and level of analysis.

RESULTS

Twelve studies were examined. There was a lack of explicit theoretical underpinning for most questionnaires and some instruments did not report standard psychometric criteria. Where this information was available, several questionnaires appeared to have limitations.

CONCLUSIONS

More consideration should be given to psychometric factors in the design of healthcare safety climate instruments, especially as these are beginning to be used in large scale surveys across healthcare organisations.

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.

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.

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.

The Effects of Repetitive Transcranial Magnetic Stimulation (rTMS) on Procedural Memory and Dysphoric Mood in Patients With Major Depressive Disorder

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.

Skill Learning: Putting Procedural Consolidation in Context

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.

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.

Studies in cognition: the problems solved and created by transcranial magnetic stimulation

The application of transcranial magnetic stimulation (TMS) to investigate important questions in cognitive neuroscience has increased considerably in the last few years. TMS can provide substantial insights into the nature and the chronometry of the computations performed by specific cortical areas during various aspects of cognition. However, the use of TMS in cognitive studies has many potential perils and pitfalls. Although TMS can help bridge the gap between psychological models and brain-based arguments of cognitive functions, hypothesis-driven carefully designed experiments that acknowledge the current limitations of TMS are critical.

A prospective study of early diagnostic investigations in the diagnosis of ankylosing spondylitis

This study was designed to assess the relative values current of locally available investigations in the early diagnosis of inflammatory sacroiliitis. Consecutive patients attending routine rheumatology clinics in Aberdeen clinically considered by consultant rheumatologists to have inflammatory back disease but with insufficient criteria to firmly establish a diagnosis of ankylosing spondylitis were included. Patients were assessed using a standard questionnaire, clinical examination of spinal movements, plain radiology of the sacroiliac joints, computerised tomographic scanning of the sacroiliac joints and HLA-B27 typing. Patients were systematically followed up using repeated clinical and radiological examination for five years. Plain film evidence of grade 2 radiological sacroiliitis (bilateral or unilateral) was found to be the most reliable predictor for the development of ankylosing spondylitis satisfying the New York criteria at 5 year follow up. CT scanning and HLA-B27 typing were of no added value in this series and the clinical questionnaire lacked specificity. It is concluded that the combination of clinical history, examination and plain film radiology are currently reliable criteria for diagnosing the subsequent development of ankylosing spondylitis satisfying established criteria.

Prefrontal cortex: procedural sequence learning and awareness

Activation of the prefrontal cortex has been linked to awareness during sequence-learning tasks. A recent study, however, finds activation of the prefrontal cortex during such tasks regardless of awareness. So what is the neurophysiological basis of awareness, and what is the role of the prefrontal cortex in sequence learning?

Aspects of sensory guidance in sequence learning

We explored the effects of sensory information upon procedural learning using three versions of the serial reaction-time task (SRTT): a standard task where the position of the stimulus cued the response; a non-standard task where the color of the stimulus was related to the correct response; and a combined task where both the color and position simultaneously cued the response. Despite these differences, each task had the same temporal pattern of a repeating ten-item sequence. We refer to each of these tasks based upon the cues available for guiding learning: position, color, and combined tasks. Procedural sequence learning was greater for the combined than for the other two tasks, suggesting that learning is enhanced when multiple sources of sensory information cue consistently and simultaneously for the same response. Transfer of skill occurred across all the tasks, except from the position to the color task. These results suggest that a fundamental neural algorithm is responsible for acquiring knowledge about a temporal sequence of responses rather than forming an associative relationship amongst stimuli.

The role of the dorsolateral prefrontal cortex during sequence learning is specific for spatial information

Many studies have implicated the dorsolateral prefrontal cortex in the acquisition of skill, including procedural sequence learning. However, the specific role it performs in sequence learning has remained uncertain. This type of skill has been intensively studied using the serial reaction time task. We used three versions of this task: a standard task where the position of the stimulus cued the response; a non-standard task where the color of the stimulus was related to the correct response; and a combined task where both the color and position simultaneously cued the response. We refer to each of these tasks based upon the cues available for guiding learning as position, color and combined tasks. The combined task usually shows an enhancement of skill acquisition, a result of being driven by two simultaneous and congruent cues. Prior to the performance of each of these tasks the function of the dorsolateral prefrontal cortex was disrupted using repetitive transcranial magnetic stimulation. This completely prevented learning within the position task, while sequence learning occurred to a similar extent in both the color and combined tasks. So, following prefrontal stimulation the expected learning enhancement in the combined task was lost, consistent with only a color cue being available to guide sequence learning in the combined task. Neither of these effects was observed following stimulation at the parietal cortex. Hence the critical role played by the dorsolateral prefrontal cortex in sequence learning is related exclusively to spatial cues. We suggest that the dorsolateral prefrontal cortex operates over the short term to retain and manipulate spatial information to allow cortical and subcortical structures to learn a predictable sequence of actions. Such functions may emerge from the broader role the dorsolateral prefrontal cortex has in spatial working memory. These results argue against the dorsolateral prefrontal cortex constituting part of the neuronal substrate responsible for general aspects of implicit or explicit sequence learning.