Physiological mechanism
The primary sensory and motor cortex has significant bilateral cross-control characteristics with the limbs; at the same time, there are a large number of transcallosal fiber connections between the equal brain regions of both hemispheres; there are also dynamic functional connections and interactions between the M1 and S1 areas of both hemispheres Inhibition, in a normal state of checks and balances.
Higher-level brain functions have obvious lateralization characteristics. For example, the cognitive processing of language, text symbols, mathematical rules, etc. has obvious left-side advantages, while spatial attention and sensory-perceptual integration have more obvious right-side advantages. Advantage.
The relationship between information exchange, functional integration, and competitive inhibition between the two hemispheres of the brain is not static, but is constantly changing. At different moments, both hemispheres can occupy dominant positions respectively, and are in a dynamic left-right check and balance.
Pathological mechanism
In most patients with stroke, the lesions are limited to one hemisphere. At this time, the normal check and balance between bilateral brain functions is broken, resulting in various abnormal patterns. The functional activity of the motor cortex on the lesion side, especially the primary motor cortex, is reduced, accompanied by an increase in the functional activity of the motor cortex on the unaffected side; the functional connection between the motor cortex on the lesion side and the contralateral hemisphere is weakened, accompanied by a reduction in the normal inhibition of the motor cortex on the contralateral side by the motor cortex on the lesion side. and overinhibition of the lesion side by the contralateral side.
normal performance
The left-right check and balance of upper limb and hand functions includes the organic combination of multiple aspects. Its normal performance mainly includes:
Ⅰ Non-purpose sports
When maintaining non-purpose movements such as posture, the left and right balance manifests itself as the coordinated balance of muscle strength, muscle tension, and limb movement trajectories.
Ⅱ Purposeful Movement
When performing various purposeful and instrumental operations, such as painting, manufacturing machinery, etc., precise coordination between the left and right sides is required.
Ⅲ Exerting sensory functions
When exerting sensory functions, the somatosensory information provided by the left and right hands is an important source of information for forming perceptual activities at the level of consciousness; it also closely cooperates with the motor functions of the hands to continuously provide real-time sensory feedback for purposeful activities.
Ⅳ Participate in cognition and other advanced brain function activities
There is a close relationship between hand function and higher brain functions such as cognition: the sensory input of the hand is an important source of information for cognitive processing; the motor function of the hand is the basis for the realization of purposeful movements; the brain areas/brain networks related to hand function , overlaps with the brain areas/brain networks responsible for high-level cognitive functions such as language.
Ⅴ Coordinating movements with other parts of the body, etc.
When normal people maintain posture, walk and other non-purpose movements, or perform purposeful movements, the upper limbs/hands and lower limbs, head and neck, trunk and other body parts need overall left and right control and balance.
Abnormal behavior
Among stroke patients, abnormalities in the left and right balance of the upper limbs and hands mainly include some typical manifestations such as hemiplegia, ataxia, coordination disorders, sensory impairments, and abnormalities in cognitive function levels.
