Cerebellar-dependent associative learning is preserved in Duchenne muscular dystrophy: a study using delay eyeblink conditioning

Brain Alteration Patterns in Children with Duchenne Muscular Dystrophy: A Machine Learning Approach to Magnetic Resonance Imaging

Background

Duchenne Muscular Dystrophy (DMD) is a genetic disease in which lack of the dystrophin protein causes progressive muscular weakness, cardiomyopathy and respiratory insufficiency. DMD is often associated with other cognitive and behavioral impairments, however the correlation of abnormal dystrophin expression in the central nervous system with brain structure and functioning remains still unclear.

Objective

To investigate brain involvement in patients with DMD through a multimodal and multivariate approach accounting for potential comorbidities.

Methods

We acquired T1-weighted and Diffusion Tensor Imaging data from 18 patients with DMD and 18 age- and sex-matched controls with similar cognitive and behavioral profiles. Cortical thickness, structure volume, fractional anisotropy and mean diffusivity measures were used in a multivariate analysis performed using a Support Vector Machine classifier accounting for potential comorbidities in patients and controls.

Results

the classification experiment significantly discriminates between the two populations (97.2% accuracy) and the forward model weights showed that DMD mostly affects the microstructural integrity of long fiber bundles, in particular in the cerebellar peduncles (bilaterally), in the posterior thalamic radiation (bilaterally), in the fornix and in the medial lemniscus (bilaterally). We also reported a reduced cortical thickness, mainly in the motor cortex, cingulate cortex, hippocampal area and insula.

Conclusions

Our study identified a small pattern of alterations in the CNS likely associated with the DMD diagnosis.

Role of cerebellar cortex in associative learning and memory in guinea pigs

Time-related cognitive function refers to the capacity of the brain to store, extract, and process specific information. Previous studies demonstrated that the cerebellar cortex participates in advanced cognitive functions, but the role of the cerebellar cortex in cognitive functions is unclear. We established a behavioral model using classical eyeblink conditioning to study the role of the cerebellar cortex in associative learning and memory and the underlying mechanisms. We performed an investigation to determine whether eyeblink conditioning could be established by placing the stimulating electrode in the middle cerebellar peduncle. Behavior training was performed using a microcurrent pulse as a conditioned stimulus to stimulate the middle cerebellar peduncle and corneal blow as an unconditioned stimulus. After 10 consecutive days of training, a conditioned response was successfully achieved in the Delay, Trace-200-ms, and Trace-300-ms groups of guinea pigs, with acquisition rates of >60%, but the Trace-400-ms and control groups did not achieve a conditioned stimulus-related blink conditioned response. It could be a good model for studying the function of the cerebellum during the establishment of eyeblink conditioning.

Combining genetics, neuropsychology and neuroimaging to improve understanding of brain involvement in Duchenne muscular dystrophy - a narrative review

Duchenne muscular dystrophy is a multifactorial disease including a cognitive phenotype. It is caused by mutations in the X-chromosomal DMD gene from which dystrophin is synthesized. Multiple isoforms of dystrophin have been identified. The full length dystrophin isoform Dp427_m is expressed predominantly in muscle. Other isoforms include: Dp427_c, Dp427_p, Dp260, Dp140, Dp116, Dp71 and Dp40. The majority of these isoforms are expressed in brain and several hypotheses exist on their role in subtypes of neurons and astrocytes. However, their function in relation to cognition remains unclear. Unlike progressive muscle wasting, cognitive involvement is not seen in all DMD patients and the severity varies greatly. To achieve a better understanding of brain involvement in DMD, a multidisciplinary approach is required. Here, we review the latest findings on dystrophin isoform expression in the brain; specific DMD-associated learning and behavioural difficulties; and imaging and spectroscopy findings relating to brain structure, networks, perfusion and metabolism. The main challenge lies in determining links between these different findings. If we can determine which factors play a role in the differentiation between severe and minor cognitive problems in DMD in the near future, we can both provide better advise for the patients and also develop targeted therapeutic interventions.

Cerebellar synapse properties and cerebellum-dependent motor and non-motor performance in Dp71-null mice

Recent emphasis has been placed on the role that cerebellar dysfunctions could have in the genesis of cognitive deficits in Duchenne muscular dystrophy (DMD). However, relevant genotype-phenotype analyses are missing to define whether cerebellar defects underlie the severe cases of intellectual deficiency that have been associated with genetic loss of the smallest product of the dmd gene, the Dp71 dystrophin. To determine for the first time whether Dp71 loss could affect cerebellar physiology and functions, we have used patch-clamp electrophysiological recordings in acute cerebellar slices and a cerebellum-dependent behavioral test battery addressing cerebellum-dependent motor and non-motor functions in Dp71-null transgenic mice. We found that Dp71 deficiency selectively enhances excitatory transmission at glutamatergic synapses formed by climbing fibers (CFs) on Purkinje neurons, but not at those formed by parallel fibers. Altered basal neurotransmission at CFs was associated with impairments in synaptic plasticity and clustering of the scaffolding postsynaptic density protein PSD-95. At the behavioral level, Dp71-null mice showed some improvements in motor coordination and were unimpaired for muscle force, static and dynamic equilibrium, motivation in high-motor demand and synchronization learning. Dp71-null mice displayed altered strategies in goal-oriented navigation tasks, however, suggesting a deficit in the cerebellum-dependent processing of the procedural components of spatial learning, which could contribute to the visuospatial deficits identified in this model. In all, the observed deficits suggest that Dp71 loss alters cerebellar synapse function and cerebellum-dependent navigation strategies without being detrimental for motor functions.

Summary: Dp71 is the most prominent dystrophin gene product in the adult brain. Here, multiple approaches including behavioral tests and electrophysiology are adopted to explore the role of Dp71 in the cerebellum.

Implicit learning deficit in children with Duchenne muscular dystrophy: Evidence for a cerebellar cognitive impairment?

This study aimed at comparing implicit sequence learning in individuals affected by Duchenne Muscular Dystrophy without intellectual disability and age-matched typically developing children. A modified version of the Serial Reaction Time task was administered to 32 Duchenne children and 37 controls of comparable chronological age. The Duchenne group showed a reduced rate of implicit learning even if in the absence of global intellectual disability. This finding provides further evidence of the involvement of specific aspects of cognitive function in Duchenne muscular dystrophy and on its possible neurobiological substrate.

Cognitive profile in Duchenne muscular dystrophy boys without intellectual disability: The role of executive functions

The aim of our prospective observational study was to assess profiles of cognitive function and a possible impairment of executive functions in a cohort of boys with Duchenne muscular dystrophy without intellectual and behavior disability. Forty Duchenne boys (range of age: 6 years to 11 years and 6 months) were assessed by Wechsler Intelligence scale and battery of tests including tasks assessing working memory and executive functions (inhibition and switching, problem solving and planning). In our cohort some aspects of cognitive function were often impaired. These included multitasking, problem solving, inhibition and working memory necessary to plan and direct goal oriented behavior. Our results support the suggestion that aspects of cognitive function could be impaired even in boys without intellectual disability and support the hypothesis that executive functions may play an important role in specific aspects of cognitive impairment in Duchenne muscular dystrophy.