The form of distribution of SCP over the surface of the head

An important issue is the correspondence of the topographic distribution of SCP on the scalp and the surface of the brain. Currently, there are ideas that the veins on the surface of the hemispheres and the diploic veins have a similar topography. Due to the presence of a limited number of graduate veins (emissaries), as well as numerous vascular connections between them, it can be assumed that the distribution of SCP on the scalp, on the skull, the dura mater and the surface of the brain will have little similarity. However, as noted above, there is a low, but significant correlation between SCPs recorded on the scalp, skull, and dura. On the other hand, it is unlikely that contact with the brain occurs through intercellular fluid, bypassing the vascular system. Two circumstances indicate this: firstly, such an electric circuit would have approximately an order of magnitude higher resistance, especially in the areas of transition from the skin to the skull and then through the bones of the skull, the dura mater, etc. and secondly, as was shown, the topography of vein graduates affects the distribution of constant potentials on the scalp .

The distribution of SCP on the surface of the head is normal in healthy adults, the right-hander has a domed shape. The maximum SCP values ​​are recorded in the vertex area. SCP values ​​in the left temporal region are higher than in the right .

Distribution of SCP on the surface of the head in righties. A – distribution of SCP in the sagittal and parasagittal directions; In – distribution of SCP in the transverse direction. z is the sagittal line, d is the right hemisphere, s is the left hemisphere. Leads: Fp – lower frontal, F – frontal, C – central, P – parietal, O – occipital, T – temporal. The location of the electrodes according to the scheme 10-20. On the ordinate axis – the magnitude of the SCP, mV, on the abscissa – the assignment of the SCP. Averaged data for 37 subjects of both sexes aged 17-19

Using ideas about the genesis of SCP, we can try to explain the shape of the distribution of constant potentials on the surface of the head. In our opinion, there are two of its determining factors: functional and anatomical. The simplest way to interpret from a functional approach is the higher SCP values ​​over the left hemisphere compared to the right. In the left, dominant in the right-handed, hemisphere, the energy exchange rate is normally higher than in the right, which leads to a higher concentration of hydrogen ions and higher values ​​of SCP.

The anatomical factor significantly affects the distribution of SCP in the norm. To understand this, some anatomical information about the venous circulation and, above all, about the venous sinuses – original vessels formed by the leaves of the dura mater, will have to be involved. The largest is the superior sagittal sinus, which runs along the upper edge of the crescent process of the dura mater from the cocks of the frontal bone to the occipital protrusion. The direct sinus is located along the junction of the sickle of the cerebrum with an outline of the cerebellum; it falls into the transverse sinus, which lies along the posterior outline of the cerebellum. The sinus drain connecting the superior sagittal, direct and transverse sinuses is located in the region of the internal occipital protrusion .

In our case, the discharge electrodes are located near large diploic veins and venous emissaries. The frontal lead is located near the frontal diploic vein, the central lead is near the parietal opening through which the parietal emissary vein connects the superior sagittal sinus to the superficial temporal vein, the occipital lead is near the occipital diploic vein, which passes through the occipital emissary into the occipital vein (occipital the vein is also connected to the transverse sinus); temporal

the lead is located in the pool of the anterior and posterior temporal temporal veins, which are connected through the corresponding emissaries to the posterior auricular vein. When the reference electrode is located on the earlobe, and the active electrodes in the temporal regions of the SCP are often close to zero, since the potential difference depends on the same vascular sources.

The influence of the sagittal sinus on the distribution of SCP is greatest in comparison with the cerebral veins located parasagittally. When registering SCP with electrodes located above the sagittal line, the electrical circuit passes through the sagittal sinus. Due to the large volume of acidic venous blood in this sinus, the value of SCP in sagittal leads is normally higher than in parasagittal leads.

The nature of SCP is unusual for classical electrophysiology: on the one hand, this is clearly an electrophysiological phenomenon, on the other hand, its genesis, when registered from the scalp, is mainly associated with the potentials of the BBB and blood vessels, and not with the membrane potentials of neurons and glia. As already mentioned, the state of acid-base equilibrium on both sides of the basement membrane has a great influence on the SCP value

BBB. Since the dynamics of pH at the BBB boundary depends on the intensity

energy processes in the brain, then SCP is an electrophysiological indicator that, when correctly recorded, reflects the ratio between blood acidities of the brain and peripheral capillaries, which allows us to normally interpret this indicator as a characteristic of cerebral energy metabolism. In pathology, changes in the acid-base balance of the brain depend on the character of the pathological process actor .

SCP, recorded directly from the brain, integrally reflects changes in the membrane potentials of nerve and glial cells. The processes associated with the activation of significant populations of neurons, for example, epileptic activity, are accompanied by a decrease in SCP, on the contrary, inhibition of neurons is reflected in the form of a positive displacement of a constant potential.

In most cases, these potentials do not make a significant contribution to the soft starter recorded on the surface of the head, since other powerful sources of constant potentials are located closer to the discharge electrodes. The presence of these generators leads to the fact that with changes in cerebral activity, shifts of SCP in the brain are accompanied by opposite in sign changes in SCP in the surface of the head.

An important source of electrical reactions in the body is the vascular system. The walls of arteries and veins function as electrical insulators surrounding an electrically conductive blood plasma; at the level of the capillaries, an electrical contact is made between blood plasma and tissue fluid, which, like plasma, is electrically conductive. The value of the potential difference at the border of the blood-brain and histo-hematological barriers depends on the concentration of hydrogen ions inside the vessel, and with acidification of the blood, the positive potential on the outside of the vessel increases and decreases on the inside. This situation arises when energy metabolism is enhanced, when acidic metabolic products accumulate in vessels (veins and capillaries). Electrical processes in the vascular system are of great importance in ensuring energy metabolism in the body.

The BBB is the most important source of potentials arising in the vascular system of the head, since the production of hydrogen ions by the brain is very high (the intensity of cerebral energy exchange is about an order of magnitude higher than in the skin), and this source has a large internal resistance. Intracranial space is connected with extracranial space through graduate veins, which allows recording the shifts of the BBB potential difference on the head surface. When registering SCP from the surface of the head, the electric circuit passes through the vascular system, since skin capillaries have much less resistance than other tissues.

The potential difference when the active electrode is located on the head, and the reference on the hand, as a rule, is positive, which is due to the significantly higher formation of acidic products during energy metabolism of the brain, compared with the tissues of the hand. When the pH flowing from the blood brain decreases, the SCP on the surface of the head increases. This can be observed with an increase in brain activity, when acidic products of energy exchange increase in the blood, as well as in other cases of acidosis of the blood flowing from the brain.

Changes in the pH in the peripheral blood also affect the value of the potential in the region of the reference electrode, as evidenced by experiments with hyperventilation in conditions of selective violation of arterial or venous outflow.

Venous sinuses, which are reservoirs of acidified venous blood and associated with extracranial space through emissive veins and diploic veins, have a certain effect on the topography of SCP on the head surface. Due to the supply of acidified venous blood from the internal jugular vein system to the extracranial space, the head regions located above the sinuses have a higher SCP.

local_offerevent_note September 13, 2019

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