Non-technical summary Neuronal plasticity refers to the ability of the brain to change in response to different experiences. Plasticity varies between people, but it is not known how much of this variability is due to differences in their genes. In humans, plasticity can be probed by a protocol termed paired associative stimulation and the changes in the motor system that are brought about by such stimulation are thought to be due to strengthening synapses which connect different neurons. We examined pairs of sisters which were either genetically identical (monozygotic) or different (dizygotic). We found that the variability within the monozygotic sister pairs was less than the variability within the dizygotic sister pairs. That plasticity in human motor cortex is in a substantial part genetically determined may be relevant for motor learning and neurorehabilitation, such as after stroke.Abstract Brain plasticity refers to changes in the organization of the brain as a result of different environmental stimuli. The aim of this study was to assess the genetic variation of brain plasticity, by comparing intrapair differences between monozygotic (MZ) and dizygotic (DZ) twins. Plasticity was examined by a paired associative stimulation (PAS) in 32 healthy female twins (9 MZ and 7 DZ pairs, aged 22.6 ± 2.7 and 23.8 ± 3.6 years, respectively). Stimulation consisted of low frequency repetitive application of single afferent electric stimuli, delivered to the right median nerve, paired with a single pulse transcranial magnetic stimulation (TMS) for activation of the abductor pollicis brevis muscle (APB). Corticospinal excitability was monitored for 30 min following the intervention. PAS induced an increase in the amplitudes of the motor evoked potentials (MEP) in the resting APB, compared to baseline. Intrapair differences, after baseline normalization, in the MEP amplitudes measured at 25-30 min post-intervention, were almost double for DZ (1.25) in comparison to MZ (0.64) twins (P = 0.036). The heritability estimate for brain plasticity was found to be 0.68. This finding implicates that genetic factors may contribute significantly to interindividual variability in plasticity paradigms. Genetic factors may be important in adaptive brain reorganization involved in motor learning and rehabilitation from brain injury.

The aim of this study was to elucidate the relative contribution of genes and environment on individual differences in motor control and acquisition of a force control task, in view of recent association studies showing that several candidate polymorphisms may have an effect on them. Forty‐four healthy female twins performed brisk isometric abductions with their right thumb. Force was recorded by a transducer and fed back to the subject on a computer screen. The task was to place the tracing of the peak force in a force window defined between 30% and 40% of the subject's maximum force, as determined beforehand. The initial level of proficiency was defined as the number of attempts reaching the force window criterion within the first 100 trials. The difference between the number of successful trials within the last and the first 100 trials was taken as a measure of motor learning. For motor control, defined by the initial level of proficiency, the intrapair differences in monozygotic (MZ) and dizygotic (DZ) twins were 6.8 ± 7.8 and 13.8 ± 8.4, and the intrapair correlations 0.77 and 0.39, respectively. Heritability was estimated at 0.68. Likewise for motor learning intrapair differences in the increment of the number of successful trials in MZ and DZ twins were 5.4 ± 5.2 and 12.8 ± 7, and the intrapair correlations 0.58 and 0.19. Heritability reached 0.70. The present findings suggest that heredity accounts for a major part of existing differences in motor control and motor learning, but uncertainty remains which gene polymorphisms may be responsible.

In this study, heredity accounted for most of the existing differences in neuromuscular coordination in fast movements. This implies that movement strategies, which are organized in the CNS and control fast movements, are also strongly genetically dependent.

Heritability studies using the twin model have provided the basis to disentangle genetic and environmental factors that contribute to several complex human traits. However, the relative importance of these factors to individual differences in proprioception is largely unknown despite the fact that proprioceptive senses are of great importance, allowing us to respond to stimuli stemming from the space around us and react to altering circumstances. Hence, a total of 44 healthy male twins (11 MZ and 11 DZ pairs), 19-28 yr old, were examined for movement, position, and force sense at the elbow joint, and their heritability estimates were computed. Results showed that genetic factors explained 1) 72 and 76% of the total variance of movement sense at the start and the end of the movement, respectively, 2) 60 to 77% of the total variance of position sense, depending on the angle of elbow flexion and whether forearm positioning was active or passive, and 3) 73 and 70% of the total variance of the force sense at 90 and 60° of elbow flexion, respectively. It is concluded that proprioception assessed by these conscious sensations is to a substantial degree genetically dependent, with heritability indexes ranging from 0.60 to 0.77, depending on the task. NEW & NOTEWORTHY Proprioceptive acuity varies among people, but it is not known how much of this variability is due to differences in their genes. This study is the first to report that proprioception, expressed as movement sense, position sense, and force sense, is substantially heritable, and it is conceivable that this may have implications for motor learning and control, neural development, and neurorehabilitation.

There is a scarcity of studies on genetic variation of essential components of neuromuscular performance, such as maximal velocity and EMG activity during maximal effort. Using the twin model and comparing intrapair differences between monozygotic (MZ) and dizygotic (DZ) twins, we derived for these neuromuscular components heritability estimates (h2), signifying the phenotypic variance due to genetic differences. A group of forty healthy male twins, 10 MZ and 10 DZ pairs, aged 21.5 +/- 2.4 and 21.0 +/- 2.1 yr, respectively, performed dynamic elbow flexion to assess maximal velocity, and maximal isometric contraction to assess EMG activity of the biceps brachii muscle. Intrapair differences for maximal velocity in MZ and DZ twins were 0.22+/- 0.04 and 0.55 +/- 0.17 m x s(-1), and intrapair correlations were 0.95 and 0.54, respectively; h2 for maximal velocity was 0.84. Likewise, intrapair differences for EMG activity during maximal isometric contraction were 0.061 +/- 0.03 in MZ and 0.176 mV in DZ; the respective intrapair correlations were 0.93 and 0.46, and h2 was 0.85. In conclusion, maximal velocity of the upper limb, using a simple movement of a single joint and EMG activity during maximal isometric contraction, seems to be highly heritable characteristics in humans.

No abstract

No abstract

No abstract