Cellular and molecular neuronal plasticity

Evidence of Neuroplastic Changes after Transcranial Magnetic, Electric, and Deep Brain Stimulation

Electric and magnetic stimulation of the human brain can be used to excite or inhibit neurons. Numerous methods have been designed over the years for this purpose with various advantages and disadvantages that are the topic of this review. Deep brain stimulation (DBS) is the most direct and focal application of electric impulses to brain tissue. Electrodes are placed in the brain in order to modulate neural activity and to correct parameters of pathological oscillation in brain circuits such as their amplitude or frequency. Transcranial magnetic stimulation (TMS) is a non-invasive alternative with the stimulator generating a magnetic field in a coil over the scalp that induces an electric field in the brain which, in turn, interacts with ongoing brain activity. Depending upon stimulation parameters, excitation and inhibition can be achieved. Transcranial electric stimulation (tES) applies electric fields to the scalp that spread along the skull in order to reach the brain, thus, limiting current strength to avoid skin sensations and cranial muscle pain. Therefore, tES can only modulate brain activity and is considered subthreshold, i.e., it does not directly elicit neuronal action potentials. In this review, we collect hints for neuroplastic changes such as modulation of behavior, the electric activity of the brain, or the evolution of clinical signs and symptoms in response to stimulation. Possible mechanisms are discussed, and future paradigms are suggested.

Traumatic brain injury modifies synaptic plasticity in newly-generated granule cells of the adult hippocampus

The hippocampus is vulnerable to traumatic brain injury (TBI), and hippocampal damage is associated with cognitive deficits that are often the hallmark of TBI. Recent studies have found that TBI induces enhanced neurogenesis in the dentate gyrus (DG) of the hippocampus, and this cellular response is related to innate cognitive recovery. However, cellular mechanisms of the role of DG neurogenesis in post-TBI recovery remain unclear. This study investigated changes in long-term potentiation (LTP) within the DG in relation to TBI-induced neurogenesis. Adult male rats received a moderate TBI or sham injury and were sacrificed for brain slice recordings at 30 or 60 days post-injury. Recordings were taken from the medial perforant path input to DG granule cells in the presence or absence of the GABAergic antagonist picrotoxin, reflecting activity of either all DG granule cells or predominately newborn granule cells, respectively. Measurements of LTP observed in the total granule cell population (with picrotoxin) showed a prolonged impairment which worsened between 30 and 60 days post-TBI. Under conditions which predominantly reflected the LTP elicited in newly born granule cells (no picrotoxin), a strikingly different pattern of post-TBI changes was observed, with a time-dependent cycle of functional impairment and recovery. At 30 days after injury this cell population showed little or no LTP, but by 60 days the capacity for LTP of the newly born granule cells was no different from that of sham controls. The time-frame of LTP improvements in the newborn cell population, comparable to that of behavioral recovery reported previously, suggests the unique functional properties of newborn granule cells enable them to contribute to restorative change following brain injury.

Brain activity changes following neuroproprioceptive "facilitation, inhibition" physiotherapy in multiple sclerosis: a parallel group randomized comparison of two approaches

BACKGROUND

Imaging methods bring new possibilities for describing the brain plasticity processes that underly the improvement of clinical function after physiotherapy in people with multiple sclerosis (pwMS). Although these processes have been described mainly in connection with task-oriented physiotherapy and aerobic training, they have not been properly verified in neuroproprioceptive "facilitation, inhibition" (facilitation) approaches.

AIM

The study determined whether facilitation physiotherapy could enhance brain plasticity, compared two facilitation methods and looked for any relation to clinical improvement in pwMS.

DESIGN

The study was designed as parallel group randomized comparison of two kinds of physiotherapeutic interventions referred to healthy controls.

SETTING

Thirty-eight outpatients were involved in the study.

POPULATION

The study had 80 participants (38 pwMS and 42 healthy controls).

METHODS

PwMS were divided into two groups and underwent a two-month physiotherapy program: Vojta reflex locomotion (VRL) or Motor program activating therapy (MPAT), (1 hour, twice a week). Functional magnetic resonance imaging (fMRI) and clinical examination was performed before and after therapy. Healthy controls underwent one fMRI examination.

RESULTS

Physiotherapy in pwMS leads to extension of brain activity in specific brain areas (cerebellum, supplementary motor areas and premotor areas) in connection with the improvement of the clinical status of individual patients after therapy (P=0.05). Greater changes (P=0.001) were registered after MPAT than after VRL. The extension of activation was a shift to the examined activation of healthy controls, whose activation was higher in the cerebellum and secondary visual area (P=0.01).

CONCLUSIONS

Neuroproprioceptive "facilitation, inhibition" physiotherapy may enhance brain activity and could involve processes connected with the processing of motion activation.

CLINICAL REHABILITATION IMPACT

The study showed that facilitation approach can modulate brain activity. This could be useful for developing of effective physiotherapeutic treatment in MS.

Does Experience Enhance Cognitive Flexibility? An Overview of the Evidence Provided by the Environmental Enrichment Studies

Neuroplasticity accounts for the ability of the brain to change in both structure and function in consequence of life experiences. An enhanced stimulation provided by the environment is able to create a form of brain, neural, and cognitive reserve, which allows an individual to cope better with the environmental demands, also in case of neural damage leading to cognitive decline. With its complex manipulation of several stimuli, the animal experimental paradigm of environmental enrichment (EE) appears particularly effective in modulating the ability to successfully respond to the ever-changing characteristics of the environment. According to this point, it could be very relevant to analyze the specific effects of EE on cognitive flexibility (CF). CF could be defined as the ability to effectively change behavior in response to the environmental condition changing. This review article is specifically aimed to summarize and focus on the available evidence in relation to the effects of EE on CF. To this aim, findings obtained in behavioral tasks specifically structured to investigate animal CF, such as reversal learning and attentional set-shifting tests (tasks based on the request of responding to a rewarding rule that changes, within one or multiple perceptual dimensions), are reviewed. Data provided on the structural and biochemical correlates of these findings are also enumerated. Studies realized in healthy animals and also in pathological models are considered. On the whole, the summarized evidence clearly supports the specific beneficial effects of EE on CF. However, further studies on this key topic are strictly required to gain a comprehensive and detailed framework on the mechanisms by which an enhanced stimulation could improve CF.

Bridging the gap: Mechanisms of plasticity and repair after pediatric TBI

Traumatic brain injury is the leading cause of death and disability in the United States, and may be associated with long lasting impairments into adulthood. The multitude of ongoing neurobiological processes that occur during brain maturation confer both considerable vulnerability to TBI but may also provide adaptability and potential for recovery. This review will examine and synthesize our current understanding of developmental neurobiology in the context of pediatric TBI. Delineating this biology will facilitate more targeted initial care, mechanism-based therapeutic interventions and better long-term prognostication and follow-up.

The interplay between neuroendocrine and sleep alterations following traumatic brain injury

BACKGROUND

Sleep and endocrine disruptions are prevalent after traumatic brain injury (TBI) and are likely to contribute to morbidity.

OBJECTIVE

To describe the interaction between sleep and hormonal regulation following TBI and elucidate the impact that alterations of these systems have on cognitive responses during the posttraumatic chronic period.

METHODS

Review of preclinical and clinical literature describing long-lasting endocrine dysregulation and sleep alterations following TBI. The bidirectional relationship between sleep and hormones is described. Literature describing co-occurrence between sleep-wake disturbances and hormonal dysregulation will be presented. Review of literature describing cognitive effects of seep and hormones. The cognitive and functional impact of sleep disturbances and hormonal dysregulation is discussed within the context of TBI.

RESULTS/CONCLUSIONS

Sleep and hormonal alterations impact cognitive and functional outcome after TBI. Diagnosis and treatment of these disturbances will impact recovery following TBI and should be considered in the post-acute rehabilitative setting.

Prevention Strategies in Post-TBI Depression in Older Adults: A Case Study

PURPOSE

The purpose of this study was to describe a theoretically focused intervention aimed toward chronic stress and depressive symptom management that is coordinated by a case manager and delivered within a home environment by the caregiver.

PRIMARY PRACTICE SETTING

Home care, community setting.

METHODS

A case study of an older adult with traumatic brain injury (TBI) secondary to a fall who had significant allostatic load at the time of his injury. "Allostatic load" is a theoretical construct that suggests the brain is experiencing chronic strain on its systems that flexibly respond to stressors. Sustained allostatic load can contribute to chronic conditions and poor outcomes.

FINDINGS

Through actions with the family as caregivers, the case manager was able to coordinate a structured home setting and gradual resumption of social activities for this older adult. Focus was on establishing structure, meaningful social interactions, and positive home experiences that maximized the older adult's interests and capacity and mitigated chronic stress. Gradually, the older adult returned to his preinjury capacity and lives independently within the family home.

IMPLICATIONS FOR CASE MANAGEMENT PRACTICE

The case management process has the potential to mitigate stressors and improve depression management through family-focused care. Although there is limited guidance on prevention of depression, this approach resulted in attainment of safe home care, no hospital readmissions, and return to previous lifestyle for the older adult. This could be useful in the prevention of post-TBI depression.

Single severe traumatic brain injury produces progressive pathology with ongoing contralateral white matter damage one year after injury

There is increasing recognition that traumatic brain injury (TBI) may initiate long-term neurodegenerative processes, particularly chronic traumatic encephalopathy. However, insight into the mechanisms transforming an initial biomechanical injury into a neurodegenerative process remain elusive, partly as a consequence of the paucity of informative pre-clinical models. This study shows the functional, whole brain imaging and neuropathological consequences at up to one year survival from single severe TBI by controlled cortical impact in mice. TBI mice displayed persistent sensorimotor and cognitive deficits. Longitudinal T2 weighted magnetic resonance imaging (MRI) showed progressive ipsilateral (il) cortical, hippocampal and striatal volume loss, with diffusion tensor imaging demonstrating decreased fractional anisotropy (FA) at up to one year in the il-corpus callosum (CC: -30%) and external capsule (EC: -21%). Parallel neuropathological studies indicated reduction in neuronal density, with evidence of microgliosis and astrogliosis in the il-cortex, with further evidence of microgliosis and astrogliosis in the il-thalamus. One year after TBI there was also a decrease in FA in the contralateral (cl) CC (-17%) and EC (-13%), corresponding to histopathological evidence of white matter loss (cl-CC: -68%; cl-EC: -30%) associated with ongoing microgliosis and astrogliosis. These findings indicate that a single severe TBI induces bilateral, long-term and progressive neuropathology at up to one year after injury. These observations support this model as a suitable platform for exploring the mechanistic link between acute brain injury and late and persistent neurodegeneration.

Neurotrauma: The Crosstalk between Neurotrophins and Inflammation in the Acutely Injured Brain

Traumatic brain injury (TBI) is a major cause of morbidity and mortality among young individuals worldwide. Understanding the pathophysiology of neurotrauma is crucial for the development of more effective therapeutic strategies. After the trauma occurs, immediate neurologic damage is produced by the traumatic forces; this primary injury triggers a secondary wave of biochemical cascades together with metabolic and cellular changes, called secondary neural injury. In the scenario of the acutely injured brain, the ongoing secondary injury results in ischemia and edema culminating in an uncontrollable increase in intracranial pressure. These areas of secondary injury progression, or areas of “traumatic penumbra”, represent crucial targets for therapeutic interventions. Neurotrophins are a class of signaling molecules that promote survival and/or maintenance of neurons. They also stimulate axonal growth, synaptic plasticity, and neurotransmitter synthesis and release. Therefore, this review focuses on the role of neurotrophins in the acute post-injury response. Here, we discuss possible endogenous neuroprotective mechanisms of neurotrophins in the prevailing environment surrounding the injured areas, and highlight the crosstalk between neurotrophins and inflammation with focus on neurovascular unit cells, particularly pericytes. The perspective is that neurotrophins may represent promising targets for research on neuroprotective and neurorestorative processes in the short-term following TBI.