Implementing Gait Kinematic Trajectory Forecasting Models on an Embedded System

Smart algorithms for gait kinematic motion prediction in wearable assistive devices including prostheses, bionics, and exoskeletons can ensure safer and more effective device functionality. Although embedded systems can support the use of smart algorithms, there are important limitations associated with computational load. This poses a tangible barrier for models with increased complexity that demand substantial computational resources for superior performance. Forecasting through Recurrent Topology (FReT) represents a computationally lightweight time-series data forecasting algorithm with the ability to update and adapt to the input data structure that can predict complex dynamics. Here, we deployed FReT on an embedded system and evaluated its accuracy, computational time, and precision to forecast gait kinematics from lower-limb motion sensor data from fifteen subjects. FReT was compared to pretrained hyperparameter-optimized NNET and deep-NNET (D-NNET) model architectures, both with static model weight parameters and iteratively updated model weight parameters to enable adaptability to evolving data structures. We found that FReT was not only more accurate than all the network models, reducing the normalized root-mean-square error by almost half on average, but that it also provided the best balance between accuracy, computational time, and precision when considering the combination of these performance variables. The proposed FReT framework on an embedded system, with its improved performance, represents an important step towards the development of new sensor-aided technologies for assistive ambulatory devices.

Hypothalamic CRH neurons represent physiological memory of positive and negative experience

Recalling a salient experience provokes specific behaviors and changes in the physiology or internal state. Relatively little is known about how physiological memories are encoded. We examined the neural substrates of physiological memory by probing CRHPVN neurons of mice, which control the endocrine response to stress. Here we show these cells exhibit contextual memory following exposure to a stimulus with negative or positive valence. Specifically, a negative stimulus invokes a two-factor learning rule that favors an increase in the activity of weak cells during recall. In contrast, the contextual memory of positive valence relies on a one-factor rule to decrease activity of CRHPVN neurons. Finally, the aversive memory in CRHPVN neurons outlasts the behavioral response. These observations provide information about how specific physiological memories of aversive and appetitive experience are represented and demonstrate that behavioral readouts may not accurately reflect physiological changes invoked by the memory of salient experiences.

A wearable device-enabled therapeutic approach to improve joint attention in autism spectrum disorder: a prospective pilot study

It has been previously proposed that interventions aimed at integrating and co-activating music processing and motor control systems could have therapeutic potential for priming social skill development in children with autism spectrum disorder (ASD). In this study, we assessed this hypothesis through a wearable sensor platform called Ambulosono ("Ambulo"-walk; "sono"-sound) in which pleasurable children's musical stimuli are contingently linked to effortful motor action (locomotor step size), thus creating a motivational state proposed to be conducive to joint attention (JA) operation. Five participants were recruited from a community-based partner and were assessed by scoring responses following therapist-directed bids for JA. Multiple assessment sessions through a repeated time-series design were conducted to determine baseline and post-intervention scores. The intervention session consisted of approximately 15 min of Ambulosono exposure. Baseline and post-intervention data were aggregated and analyzed using a linear mixed-effect model. The wearable sensor and wireless headphones of the Ambulosono system were tolerated by the participants, and there were no adverse effects associated with the use of the device. We found an increase in the average responses to bids for JA during the Ambulosono intervention phase compared to baseline across participants. This increase did not appear to result from enhanced general arousal. Our pilot data support feasibility and further testing of Ambulosono as a therapeutic aid for integration into community-based ASD programs to augment shared child-therapist social interactions.

Walking exercise alters pedunculopontine nucleus connectivity in Parkinson’s disease in a dose-dependent manner

Background

Gait disturbances are critical motor symptoms in Parkinson’s disease (PD). The mechanisms of gait impairment in PD are not entirely understood but likely involve changes in the Pedunculopontine Nucleus (PPN), a critical locomotion center, and its associated connections. Exercise is universally accepted as helpful in PD, but the extent and intensity of exercise required for plastic changes are unclear.

Methods

Twenty-seven PD subjects participated in a 3-month gait training intervention. Clinical assessments and resting-state functional magnetic resonance imaging were performed at baseline and 3 months after exercise. Functional connectivity of PPN was assessed by combining the methods of partial least squares, conditional dependence and partial correlation. In addition, paired t-tests were used to examine the effect of exercise on PPN functional connectivity and clinical measures, and Pearson’s correlation was used to assess the association between altered PPN functional connectivity and clinical measures.

Results

Exercise significantly improved Unified Parkinson’s Disease Rating Scale-III (UPDRS-III). A significant increase in right PPN functional connectivity was observed after exercise, which did not correlate with motor improvement. However, the decrease in left PPN functional connectivity significantly correlated with the improvement in UPDRS-III and was linearly related to both number of walks and the duration of walks. In addition, exercise induced a significant increase in the laterality of PPN connectivity strength, which correlated with motor improvement.

Conclusion

PPN functional connectivity is modifiable by walking exercise in both a dose-independent (right PPN and laterality of PPN connectivity strength) and dose-dependent (left PPN) manner. The PPN may contribute to pathological and compensatory processes in PD gait control. The observed gait improvement by walking exercise is most likely due to the reversal of the maladaptive compensatory mechanism. Altered PPN functional connectivity can be a marker for exercise-induced motor improvement in PD.

A versatile computational algorithm for time-series data analysis and machine-learning models

Here we introduce Local Topological Recurrence Analysis (LoTRA), a simple computational approach for analyzing time-series data. Its versatility is elucidated using simulated data, Parkinsonian gait, and in vivo brain dynamics. We also show that this algorithm can be used to build a remarkably simple machine-learning model capable of outperforming deep-learning models in detecting Parkinson’s disease from a single digital handwriting test.

Visual Gait Lab: A user-friendly approach to gait analysis

BACKGROUND

Gait analysis forms a critical part of many lab workflows, ranging from those interested in preclinical neurological models to others who use locomotion as part of a standard battery of tests. Unfortunately, while paw detection can be semi-automated, it becomes generally a time-consuming process with error corrections. Improvement in paw tracking would aid in better gait analysis performance and experience.

NEW METHOD

Here we show the use of Visual Gait Lab (VGL), a high-level software with an intuitive, easy to use interface, that is built on DeepLabCut™. VGL is optimized to generate gait metrics and allows for quick manual error corrections. VGL comes with a single executable, streamlining setup on Windows systems. We demonstrate the use of VGL to analyze gait.

RESULTS

Training and evaluation of VGL were conducted using 200 frames (80/20 train-test split) of video from mice walking on a treadmill. The trained network was then used to visually track paw placements to compute gait metrics. These are processed and presented on the screen where the user can rapidly identify and correct errors.

COMPARISON WITH EXISTING METHODS

Gait analysis remains cumbersome, even with commercial software due to paw detection errors. DeepLabCut™ is an alternative that can improve visual tracking but is not optimized for gait analysis functionality.

CONCLUSIONS

VGL allows for gait analysis to be performed in a rapid, unbiased manner, with a set-up that can be easily implemented and executed by those without a background in computer programming.

The Effects of Music-Contingent Gait Training on Cognition and Mood in Parkinson Disease: A Feasibility Study

Background. In Parkinson disease (PD), gait impairments often coexist with nonmotor symptoms such as anxiety and depression. Biofeedback training may improve gait function in PD, but its effect on nonmotor symptoms remains unclear. This study explored the cognitive and global effects of Ambulosono, a cognitive gait training method utilizing step size to contingently control the real-time play of motivational music. Objective. This study examined the feasibility of music-contingent gait training and its effects on neuropsychological test performance and mood in persons with PD. Methods. A total of 30 participants with mild to moderate PD were semirandomized via sequential alternating assignment into an experimental training group or control music group. The training group received 12 weeks of music-contingent training, whereby music play was dependent on the user achieving a set stride length, adjusted online based on individual performance. The control group received hybrid training beginning with 6 weeks of noncontingent music walking, whereby music played continuously regardless of step size, followed by 6 weeks of music-contingent training. Global cognition, memory, executive function, attention, and working memory assessments were completed by blinded assessors at baseline, 6 weeks, and 12 weeks. Motor function, mood, and anxiety were assessed. Results. Average training adherence was 97%, with no falls occurring during training sessions. Improvements on cognitive measures were not clinically significant; however, significant decreases in depression and anxiety were observed in both groups over time (P < .05). Conclusions. Music-contingent gait training is feasible and safe in individuals with PD. Further investigation into potential therapeutic applications of this technology is recommended.

Muscarinic acetylcholine receptor-dependent persistent activity of layer 5 intrinsic-bursting and regular-spiking neurons in primary auditory cortex

Cholinergic signaling coupled to sensory-driven neuronal depolarization is essential for modulating lasting changes in deep-layer neural excitability and experience-dependent plasticity in the primary auditory cortex. However, the underlying cellular mechanism(s) associated with coincident cholinergic receptor activation and neuronal depolarization of deep-layer cortical neurons remains unknown. Using in vitro whole cell patch-clamp recordings targeted to neurons (n = 151) in isolated brain slices containing the primary auditory cortex (AI), we investigated the effects of cholinergic receptor activation and neuronal depolarization on the electrophysiological properties of AI layer 5 intrinsic-bursting and regular-spiking neurons. Bath application of carbachol (5 µM; cholinergic receptor agonist) paired with suprathreshold intracellular depolarization led to persistent activity in these neurons. Persistent activity may involve similar cellular mechanisms and be generated intrinsically in both intrinsic-bursting and regular-spiking neurons given that it 1) persisted under the blockade of ionotropic glutamatergic (kynurenic acid, 2 mM) and GABAergic receptors (picrotoxin, 100 µM), 2) was fully blocked by both atropine (10 µM; nonselective muscarinic antagonist) and flufenamic acid [100 µM; nonspecific Ca²⁺-sensitive cationic channel (CAN) blocker], and 3) was sensitive to the voltage-gated Ca²⁺ channel blocker nifedipine (50 µM) and Ca²⁺-free artificial cerebrospinal fluid. Together, our results support a model through which coincident activation of AI layer 5 neuron muscarinic receptors and suprathreshold activation can lead to sustained changes in layer 5 excitability, providing new insight into the possible role of a calcium-CAN-dependent cholinergic mechanism of AI cortical plasticity. These findings also indicate that distinct streams of auditory processing in layer 5 intrinsic-bursting and regular-spiking neurons may run in parallel during learning-induced auditory plasticity.NEW & NOTEWORTHY Cholinergic signaling coupled to sensory-driven neuronal depolarization is essential for modulating lasting changes in experience-dependent plasticity in the primary auditory cortex. Cholinergic activation together with cellular depolarization can lead to persistent activity in both intrinsic-bursting and regular-spiking layer 5 pyramidal neurons. A similar mechanism involving muscarinic acetylcholine receptor, voltage-gated Ca²⁺ channel, and possible Ca²⁺-sensitive nonspecific cationic channel activation provides new insight into our understanding of the cellular mechanisms that govern learning-induced auditory cortical and subcortical plasticity.

Wearable technological platform for multidomain diagnostic and exercise interventions in Parkinson's disease

Physical activity and exercise have become a central component of medical management of chronic illness, particular for the elderly who suffer from neurodegenerative disorders that impair their cognition and mobility. This chapter summarizes our recent research showing that a new generation of wearable technology can be adopted as diagnostic and rehabilitation tools for people living with Parkinson's disease. For example, wearable device-enabled 6-min walking test can be automated to eliminate human supervision and many other technical factors that confound the results with conventional testing. With reduced cost and increased test standardization, the technology can be adopted for population-based screening of cardiovascular fitness and gait rehabilitation training efficacy associated with many medical conditions. The Ambulosono platform for multidomain exercise intervention, in particular, has the potential to deliver lasting clinical benefits in slowing PD progression. The platform, through the integration of brisk walking with behavioral shaping strategies such as contingency reinforcement, anticipatory motor control and musical motivational stimulation, creates a home exercise regime that can transform monotonous walking into a pleasurable daily activity and habit.

Differentiating cognitive or motor dimensions associated with the perception of fall-related self-efficacy in Parkinson's disease

In Parkinson's disease (PD), concurrent declines in cognitive and motor domain function can severely limit an individual's ability to conduct daily tasks. Current diagnostic methods, however, lack precision in differentiating domain-specific contributions of cognitive or motor impairments based on a patients' clinical manifestation. Fear of falling (FOF) is a common clinical manifestation among the elderly, in which both cognitive and motor impairments can lead to significant barriers to a patients' physical and social activities. The present study evaluated whether a set of analytical and machine-learning approaches could be used to help delineate boundary conditions and separate cognitive and motor contributions to a patient's own perception of self-efficacy and FOF. Cognitive and motor clinical scores, in conjunction with FOF, were collected from 57 Parkinson's patients during a multi-center rehabilitation intervention trial. Statistical methodology was used to extract a subset of uncorrelated cognitive and motor components associated with cognitive and motor predictors, which were then used to independently identify and visualize cognitive and motor dimensions associated with FOF. We found that a central cognitive process, extracted from tests of executive, attentional, and visuoperceptive function, was a unique and significant independent cognitive predictor of FOF in PD. In addition, we provide evidence that the approaches described here may be used to computationally discern specific types of FOF based on separable cognitive or motor models. Our results are consistent with a contemporary model that the deterioration of a central cognitive mechanism that modulates self-efficacy also plays a critical role in FOF in PD.

Mechanisms of Hierarchical Cortical Maturation

Cortical information processing is structurally and functionally organized into hierarchical pathways, with primary sensory cortical regions providing modality specific information and associative cortical regions playing a more integrative role. Historically, there has been debate as to whether primary cortical regions mature earlier than associative cortical regions, or whether both primary and associative cortical regions mature simultaneously. Identifying whether primary and associative cortical regions mature hierarchically or simultaneously will not only deepen our understanding of the mechanisms that regulate brain maturation, but it will also provide fundamental insight into aspects of adolescent behavior, learning, neurodevelopmental disorders and computational models of neural processing. This mini-review article summarizes the current evidence supporting the sequential and hierarchical nature of cortical maturation, and then proposes a new cellular model underlying this process. Finally, unresolved issues associated with hierarchical cortical maturation are also addressed.

A training approach to improve stepping automaticity while dual-tasking in Parkinson's disease: A prospective pilot study

BACKGROUND

Deficits in motor movement automaticity in Parkinson's disease (PD), especially during multitasking, are early and consistent hallmarks of cognitive function decline, which increases fall risk and reduces quality of life. This study aimed to test the feasibility and potential efficacy of a wearable sensor-enabled technological platform designed for an in-home music-contingent stepping-in-place (SIP) training program to improve step automaticity during dual-tasking (DT).

METHODS

This was a 4-week prospective intervention pilot study. The intervention uses a sensor system and algorithm that runs off the iPod Touch which calculates step height (SH) in real-time. These measurements were then used to trigger auditory (treatment group, music; control group, radio podcast) playback in real-time through wireless headphones upon maintenance of repeated large amplitude stepping. With small steps or shuffling, auditory playback stops, thus allowing participants to use anticipatory motor control to regain positive feedback. Eleven participants were recruited from an ongoing trial (Trial Number: ISRCTN06023392). Fear of falling (FES-I), general cognitive functioning (MoCA), self-reported freezing of gait (FOG-Q), and DT step automaticity were evaluated.

RESULTS

While we found no significant effect of training on FES-I, MoCA, or FOG-Q, we did observe a significant group (music vs podcast) by training interaction in DT step automaticity (P<0.01).

CONCLUSION

Wearable device technology can be used to enable musically-contingent SIP training to increase motor automaticity for people living with PD. The training approach described here can be implemented at home to meet the growing demand for self-management of symptoms by patients.

Somato-dendritic decoupling as a novel mechanism for protracted cortical maturation

BACKGROUND

Both human and animal data indicate that disruption of the endogenously slow maturation of temporal association cortical (TeA) networks is associated with abnormal higher order cognitive development. However, the neuronal mechanisms underlying the endogenous maturation delay of the TeA are poorly understood.

RESULTS

Here we report a novel form of developmental plasticity that is present in the TeA. It was found that deep layer TeA neurons, but not hippocampal or primary visual neurons, exist in a protracted 'embryonic-like' state through a mechanism involving reduced somato-dendritic communication and a non-excitable somatic membrane. This mechanism of neural inactivity is present in intact tissue and shows a remarkable transition into an active somato-dendritically coupled state. The quantity of decoupled cells diminishes in a protracted and age-dependent manner, continuing into adolescence.

CONCLUSIONS

Based on our data, we propose a model of neural plasticity through which protracted compartmentalization and decoupling in somato-dendritic signalling plays a key role in controlling how excitable neurons are incorporated into recurrent cortical networks independent of neurogenesis.

Development and testing of a new system for assessing wheel-running behaviour in rodents

Background

Wheel running is one of the most widely studied behaviours in laboratory rodents. As a result, improved approaches for the objective monitoring and gathering of more detailed information is increasingly becoming important for evaluating rodent wheel-running behaviour. Here our aim was to develop a new quantitative wheel-running system that can be used for most typical wheel-running experimental protocols.

Findings

Here we devise a system that can provide a continuous waveform amenable to real-time integration with a high-speed video ideal for wheel-running experimental protocols. While quantification of wheel running behaviour has typically focused on the number of revolutions per unit time as an end point measure, the approach described here allows for more detailed information like wheel rotation fluidity, directionality, instantaneous velocity, and acceleration, in addition to total number of rotations, and the temporal pattern of wheel-running behaviour to be derived from a single trace. We further tested this system with a running-wheel behavioural paradigm that can be used for investigating the neuronal mechanisms of procedural learning and postural stability, and discuss other potentially useful applications.

Conclusions

This system and its ability to evaluate multiple wheel-running parameters may become a useful tool for screening new potentially important therapeutic compounds related to many neurological conditions.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-2059-6) contains supplementary material, which is available to authorized users.

Duration sensitivity of neurons in the primary auditory cortex of albino mouse

Many neurons in the central auditory system of a number of species have been found to be sensitive to the duration of sound stimuli. While previous studies have shown that γ-aminobutyric acid (GABA)-ergic inhibitory input is important for duration sensitivity in the inferior colliculus (IC), it is still unknown whether (GABA)-ergic inhibitory input plays an important role in generating duration sensitivity in the cortex. Using free-field sound stimulation and in vivo extracellular recording, we investigated duration sensitivity in primary auditory cortical (AI) neurons of the Nembutal anesthetized albino mouse (Mus musculus, Km) and examined the effect of the GABAA receptor antagonist bicuculline on AI neuron duration sensitivity. A total of 63 duration tuning curves were measured in AI neurons. Of these, 44% (28/63) exhibited duration sensitive responses, while 43% (27/63) lacked duration sensitivity. The remaining 13% (8/63) exhibited long-pass properties likely reflecting both duration sensitive and insensitive features. We found that duration sensitive neurons had shorter first spike latency (FSL) and longer firing duration (FD) when stimulated with best duration (p < 0.05), while duration insensitive neurons had invariable FSL and FD at different sound durations (p>0.05). Furthermore, 60% (6/10) of duration sensitive neurons and 75% (3/4) long-pass neurons lost duration sensitivity following bicuculline application. Taken together, our results show that cortical neurons in the albino mouse are sensitive to sound duration, and that GABAergic inhibition may play an important role in the formation of de novo duration sensitivity in AI. The possible mechanism and behavioral significance of duration sensitivity in AI neurons is discussed.

Concurrent arm swing-stepping (CASS) can reveal gait start hesitation in Parkinson's patients with low self-efficacy and fear of falling

BACKGROUND

Movement incoordination, freezing of gait, fear of falling, low self-efficacy, and multi-tasking can all contribute to falls in Parkinson's disease. How these multi-factorial risks interact in individual patients remain poorly understood.

METHODS

Concurrent arm swing-stepping is a simple motor test in which subjects are first asked to swing their arms before being instructed to initiate the secondary task of leg stepping-in-place. We postulated that in patients with multiple fall risks, sensorimotor impairments in upper- and lower-limb movement control can render concurrent arm swing-stepping a demanding dual task, thereby triggering gait hesitation. A total of 31 subjects with Parkinson's disease were enrolled in the study.

RESULTS

It was found that concurrent arm swing-stepping induced hesitation primarily in Parkinson's disease patients with low fall-related self-efficacy and a fear of falling. By contrast, concurrent arm swing-stepping led to limb incoordination in both patients and in healthy elderly controls. The calculated specificity and sensitivity of the concurrent arm swing-stepping test was 100 and 42 % for hesitation and 12 and 77 % for incoordination.

CONCLUSION

These results suggest that the concurrent arm swing-stepping test can be used in conjunction with conventional psychometric assessments to facilitate multi-factorial assessment of potential fall risk.

The single-leg-stance test in Parkinson's disease

Background

Timed single-leg-stance test (SLST) is widely used to assess postural control in the elderly. In Parkinson’s disease (PD), it has been shown that an SLST around 10 seconds or below may be a sensitive indicator of future falls. However, despite its role in fall risk, whether SLST times around 10 seconds marks a clinically important stage of disease progression has largely remained unexplored.

Methods

A cross-sectional study where 27 people with PD were recruited and instructed to undertake timed SLST for both legs was conducted. Disease motor impairment was assessed with the Unified Parkinson’s Disease Rating Scale Part 3 (UPDRS-III).

Results

This study found that: 1) the SLST in people with PD shows good test-retest reliability; 2) SLST values can be attributed to two non-overlapping clusters: a low (10.4 ± 6.3 seconds) and a high (47.6 ± 11.7 seconds) value SLST group; 3) only the low value SLST group can be considered abnormal when age-matched normative SLST data are taken into account for comparison; and 4) lower UPDRS-III motor performance, and the bradykinesia sub-score in particular, are only associated with the low SLST group.

Conclusion

These results lend further support that a low SLST time around 10 seconds marks a clinically important stage of disease progression with significant worsening of postural stability in PD.

Auditory-cued sensorimotor task reveals disengagement deficits in rats exposed to the autism-associated teratogen valproic acid

Autism Spectrum Disorder (ASD) is often found to co-exist with non-core behavioral manifestations that include difficulties in disengagement of attention to sensory cues. Here we examined whether this behavioral abnormality can be induced in rats prenatally exposed to valproic acid (VPA), a well-established teratogen associated with ASD animal models. We tested rats using an auditory-cued sensorimotor task (ACST) based on the premise that ACST will be more sensitive to developmental changes in temporal association cortex (TeA) of the posterior attention system. We show that VPA rats learned the ACST markedly faster than control animals, but they exhibited a profound preoccupation with cues associated with the expectancy at the reward location such that disengagement was disrupted. Control rats on the other hand were able to disengage and utilize auditory cues for re-engagement. However, both control and VPA-treated rats performed similarly when tested on novel object recognition (NOR) and novel context mismatch (NOCM) behavioral tasks that are known to be sensitive to normal perirhinal and prefrontal network functioning respectively. Consistent with disrupted posterior rather than frontal networks, we also report that VPA can selectively act on deep-layer TeA cortical neurons by showing that VPA increased dendritic density in isolated deep-layer TeA but not frontal neurons. These results describe a useful approach to examine the role of cue-dependent control of attention systems in rodent models of autism and suggest that disengagement impairments may arise from an inability to modify behavior through the appropriate use of sensory cue associations.

Alterations of neocortical development and maturation in autism: insight from valproic acid exposure and animal models of autism

Autism spectrum disorder (ASD) is a behaviourally defined brain disorder affecting approximately 1 in 88 children. Many pathological studies have shown that ASD is frequently associated with grey and white matter changes that can be described by their deviations from the normal trajectory of cortical maturation. For example, during the early (i.e. <2 years) postnatal period there is marked and selective tissue overgrowth in the higher-order temporal and frontal networks involved in emotional, social, and communication functions. In this focused review we first summarize some basic principles of neocortical neural organization and how they are disrupted in ASD. We will then highlight some of the potential mechanisms by which the normal developmental trajectory and organization of neocortical networks can be altered based on animal studies of valproic acid, a teratogen widely used in animal models of ASD. We argue that the trajectory of postnatal cerebral neocortex development may be influenced by several cellular and molecular mechanisms that may all converge to produce a neuropathology characterized by premature or accelerated neuronal growth.

Altering the trajectory of early postnatal cortical development can lead to structural and behavioural features of autism

BACKGROUND

Autism is a behaviourally defined neurodevelopmental disorder with unknown etiology. Recent studies in autistic children consistently point to neuropathological and functional abnormalities in the temporal association cortex (TeA) and its associated structures. It has been proposed that the trajectory of postnatal development in these regions may undergo accelerated maturational alterations that predominantly affect sensory recognition and social interaction. Indeed, the temporal association regions that are important for sensory recognition and social interaction are one of the last regions to mature suggesting a potential vulnerability to early maturation. However, direct evaluation of the emerging hypothesis that an altered time course of early postnatal development can lead to an ASD phenotype remains lacking.

RESULTS

We used electrophysiological, histological, and behavioural techniques to investigate if the known neuronal maturational promoter valproate, similar to that in culture systems, can influence the normal developmental trajectory of TeA in vivo. Brain sections obtained from postnatal rat pups treated with VPA in vivo revealed that almost 40% of cortical cells in TeA prematurely exhibited adult-like intrinsic electrophysiological properties and that this was often associated with gross cortical hypertrophy and a reduced predisposition for social play behaviour.

CONCLUSIONS

The co-manifestation of these functional, structural and behavioural features suggests that alteration of the developmental time course in certain high-order cortical networks may play an important role in the neurophysiological basis of autism.

What is the optimal value of the g-ratio for myelinated fibers in the rat CNS? A theoretical approach

BACKGROUND

The biological process underlying axonal myelination is complex and often prone to injury and disease. The ratio of the inner axonal diameter to the total outer diameter or g-ratio is widely utilized as a functional and structural index of optimal axonal myelination. Based on the speed of fiber conduction, Rushton was the first to derive a theoretical estimate of the optimal g-ratio of 0.6 [1]. This theoretical limit nicely explains the experimental data for myelinated axons obtained for some peripheral fibers but appears significantly lower than that found for CNS fibers. This is, however, hardly surprising given that in the CNS, axonal myelination must achieve multiple goals including reducing conduction delays, promoting conduction fidelity, lowering energy costs, and saving space.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we explore the notion that a balanced set-point can be achieved at a functional level as the micro-structure of individual axons becomes optimized, particularly for the central system where axons tend to be smaller and their myelin sheath thinner. We used an intuitive yet novel theoretical approach based on the fundamental biophysical properties describing axonal structure and function to show that an optimal g-ratio can be defined for the central nervous system (approximately 0.77). Furthermore, by reducing the influence of volume constraints on structural design by about 40%, this approach can also predict the g-ratio observed in some peripheral fibers (approximately 0.6).

CONCLUSIONS/SIGNIFICANCE

These results support the notion of optimization theory in nervous system design and construction and may also help explain why the central and peripheral systems have evolved different g-ratios as a result of volume constraints.

Functional architecture and spike timing properties of corticofugal projections from rat ventral temporal cortex

Sensory association and parahippocampal cortex in the ventral temporal lobe plays an important role in sensory object recognition and control of top-down attention. Although layer V neurons located in high-order cortical structures project to multiple cortical and subcortical regions, the architecture and functional organization of this large axonal network are poorly understood. Using a large in vitro slice preparation, we examined the functional organization and spike timing properties of the descending layer V axonal network. We found that most, if not all, layer V neurons in this region can form multiple axonal pathways that project to many brain structures, both proximal and remote. The conduction velocities of different axonal pathways are highly diverse and can vary up to more than threefold. Nevertheless for those axonal projections on the ipsilateral side, the speeds of axonal conduction appear to be tuned to their length. As such, spike delivery becomes nearly isochronic along these pathways regardless of projection distance. In contrast, axons projecting to the contralateral hemisphere are significantly slower and do not participate in this lateralized isochronicity. These structural and functional features of layer V network from the ventral temporal lobe may play an important role in top-down control of sensory cue processing and attention.

Axonal and somatic filtering of antidromically evoked cortical excitation by simulated deep brain stimulation in rat brain

Antidromic cortical excitation has been implicated as a contributing mechanism for high-frequency deep brain stimulation (DBS). Here, we examined the reliability of antidromic responses of type 2 corticofugal fibres in rat over a stimulation frequency range compatible to the DBS used in humans. We activated antidromically individual layer V neurones by stimulating their two subcortical axonal branches. We found that antidromic cortical excitation is not as reliable as generally assumed. Whereas the fast conducting branches of a type 2 axon in the highly myelinated brainstem region follow high-frequency stimulation, the slower conducting fibres in the poorly myelinated thalamic region function as low-pass filters. These fibres fail to transmit consecutive antidromic spikes at the beginning of high-frequency stimulation, but are able to maintain a steady low-frequency (6-12 Hz) spike output during the stimulation. In addition, antidromic responses evoked from both branches are rarely present in cortical neurones with a more hyperpolarized membrane potential. Our data indicate that axon-mediated antidromic excitation in the cortex is strongly influenced by the myelo-architecture of the stimulation site and the excitability of individual cortical neurones.

Skp2 gene copy number aberrations are common in non-small cell lung carcinoma, and its overexpression in tumors with ras mutation is a poor prognostic marker

PURPOSE

Skp2 plays a critical role in cell cycle progression, especially at the G(1)-S transition, putatively through its control of several cell cycle regulator proteins. The Skp2 gene is located on a region of chromosome 5p that is commonly overrepresented in lung cancer. The present study aimed to evaluate Skp2 abnormalities and their prognostic value in non-small cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

In total 16 NSCLC cell lines and 163 primary tumors were included in studies to measure Skp2 relative gene copy number, mRNA abundance, and protein level. The tumors were also evaluated for p27 protein expression level and ras mutation. These values were correlated with the clinical and pathological features of the patients.

RESULTS

Skp2 relative gene copy number aberrations were found in 88 and 65% of NSCLC cell lines and primary tumors, respectively. Overrepresentation was especially common among squamous cell carcinoma (74%). Both gene copy overrepresentation (13%) and loss (35%) were found in adenocarcinoma. Skp2 relative gene copy number was significantly correlated with mRNA and protein levels, but none of these were correlated with p27 protein levels. Neither high Skp2 protein expression nor ras mutation was prognostically significant. In NSCLCs with ras mutation, however, high Skp2 protein expression was a significant independent poor prognostic marker.

CONCLUSION

There appears to be a synergistic interaction between high Skp2 protein expression and ras mutation with negative impact on the survival of NSCLC patients.