Thermoimaging of the brain.

A new method of neuroimaging is proposed that is based on the recording of weak changes in infra-red radiation from the brain. Thermoencephaloscopy (TES) uses a combination of thermovision and digital image processing techniques and allows one to make a dynamic investigation of the thermal fields of the cerebral cortex through an unopened skull. Today the method is characterized by: (i) differential thermosensitivity of up to 0.002 degrees C; (ii) instrumental temporal resolution 40 ms (25 thermomaps/s); (iii) time of the temperature measurement in the part of an object that correspondes to one pixel on digital thermomap is equal to 2.4 microseconds; (iv) instrumental spatial resolution of up to 70 microns/pixel; and (v) the thermomap size is 10880 pixels (128 x 85). TES allows detection of an appearance and study of topography and dynamics of the small (from 140 to 300 microns) and precisely localized zones of activation or deactivation of the cerebral cortex that are modally and regionally specific with respect to stimuli modality and parameters and to the state of an animal. Up to now such studies were performed with white rats, rabbits, cats, monkeys and humans under different kinds of sensory stimulation, motor tasks, conditioning (associative learning). Fast thermowaves spreading over the brain cortex along specific trajectories were revealed under sensory stimulation. The mechanisms of the recorded phenomena are discussed: (i) joule heating produced by ion currents through membranes of activated neurones; (ii) metabolic thermoproduction; (iii) thermal convection by the local cerebral blood flow; and (iv) thermodipole formation in the cortical foci with changed lCBF.

Bicuculline-induced neocortical epileptiform foci and the effects of 6-hydroxydopamine in developing rats.

Catecholamines (dopamine and norepinephrine) are considered to be predominantly inhibitory neurotransmitters in the brain and their depletion produced by 6-hydroxydopamine may result in proconvulsant effects. In our experiments on rats aged 5, 7, 9, 12, 15, 18, 25 and 90 days under urethane anesthesia we demonstrated the development of neocortical epileptic focus evoked by topical application of bicuculline methiodide. In experimental groups aged 7, 12, 18, 25 and 90 days a chronic depletion of catecholamines was induced using pretreatment with 6-hydroxydopamine early postnatally. An epileptogenic focus was induced in all age groups; duration of a single discharge decreased with age in both control and experimental animals. The spread of activity from the primary focus to contralateral frontal cortex via callosal connections was as rapid as in controls. However, the transfer of discharge to occipital regions was delayed and the number of discharges decreased in experimental rats. Our study demonstrated a substantial role of catecholamines for synchronization of focal discharges in neocortex and a promoting role of catecholamines in association pathways within neocortex.

Dynamic infrared functional mapping of the cerebral cortex.

Although many neuroimaging methods (computer tomography, H+ and isotope clearance, [14C]deoxyglucose utilization, potential-sensitive dyes, electroencephalogram and magnetoencephalogram-mapping, nuclear magnetic resonance tomography, single photon emission computer tomography, and positron emission tomography) are now being used to map brain structure and function, there still exists a need for a new approach that is functional, dynamic, remote, and noninvasive, and that also has reasonable sensitivity and spatial and temporal resolution. Such a method is described here. Thermoencephaloscopy (TES), based on thermovision and digital image processing techniques, is a method of neuroimaging consisting of recording through the intact skull the very weak changes in infrared radiation that are connected with brain activity. The parameters of the method are: temperature sensitivity of 0.002 degrees C, instrumental spatial resolution of 70 microns pixel-1, and instrumental temporal resolution of 40 ms (enabling up to twenty-five maps to be produced per second). The distribution over the rat cerebral cortex of local, multiple, and modally and regionally specific thermoresponses to various sensory stimuli, direct cortical stimulation, and associative learning (conditioning), have been studied, as well as the spreading of thermowaves over the brain cortex. The underlying mechanisms which form the basis of the technique of TES, such as joule heating, local changes in brain metabolism and local cerebral blood flow, as well as the formation of thermodipoles, are discussed.

[The cholinergic system of the forebrain modulates the activity of the GABA-ergic interneurons which realize presynaptic regulation in the neocortex of kittens]. / Kholinergicheskaia sistema perednego mozga moduliruet aktivnost' GAMKergicheskikh interneironov, osushchestvliaiushchikh presinapticheskuiu reguliatsiiu v neokortekse u kotiat.

It has been found that at the end of the second week of postnatal life, stimulation of cholinergic ascending paths causes a selective inhibition of cortical neurones reaction to sensory stimulation, without influencing the background activity. The observed inhibition is blocked both by atropine and picrotoxin, but not by bicuculline. It is suggested that the observed phenomenon characterizes, presynaptic control of cortical neurones activity in the early ontogenesis. This inhibition is formed on the basis of cooperative choline- and GABA-ergic brain systems participation and is performed not through GABA-receptors.

[Temperature distribution on the surface of the rat brain during direct electric stimulation]. / Raspredelenie temperatur na poverkhnosti kory mozga krysy pri priamoi élektricheskoi stimuliatsii.

Dynamics of spatial temperature distribution over the dorsal surface of the cerebral cortex was studied through the skull with the thermovision technique on immobilized white rats. Direct cortical stimulation revealed local thermoresponses (up to +0.2 degrees C) under electrodes, in the symmetrical point in the opposite hemisphere as well as in some other cortical zones. The response latency was within the limit of 160 ms, peak latency--2-5 s and relaxation time 2-3 min. Nembutal caused depression of thermoresponses, increase in their thresholds, limitation in size as well as slowing down of the development and prolongation in time.

[Cholinergic regulation of the activity of somatosensory cortex neurons during early postnatal ontogeny of the cat]. / Kholinergicheskaia reguliatsiia aktivnosti neironov somatosensornoi kory v rannem postnatal'nom ontogeneze koshki.

In 11-14 days kittens, about 20% of neurones in the somatosensory cortical zone react to stimulation of subpallidal region which is a source of cholinergic projections to the cerebral cortex. The effect of subpallidal region stimulation is reproduced in case of microiontophoretic acetylcholine application and blocked by atropine what points to its cholinergic nature. Cholinergic stimulation causes inhibition of the background and evoked activities of the cortical neurones while, as it is known, in adult cats, acetylcholine mainly stimulates a reaction of activation. It is postulated that in kittens at the end of the second week of postnatal development, cholinergic innervation of the cortex significantly differs from the definitive one by its quantitative and functional parameters.

[Spatial characteristics and the dynamics of the activation foci in the cortex during the elaboration of a conditioned reflex (thermographic research)]. / Prostranstvennye kharakteristiki i dinamika ochagov aktivatsii v kore pri vyrabotke uslovnogo refleksa (termograficheskie issledovaniia).

In acute experiments on immobilized white rats, by thermovision methods and digital image processing, spatial distribution and dynamics of local heating and cooling of dorsal surface of the cerebral cortex was studied through intact skull during elaboration of a conditioned reflex. Distant and noninvasive thermovision methods allowed to reveal and quantitatively study local cortical thermal reactions in the somatosensory and motor cortex and in the cerebellum in the process of elaboration and testing of conditioned connection. Under discussion are mechanisms, properties and significance of these effects for investigation of learning.

[Detection of the activation of the motor cortex of the cat during movement of an extremity using thermomapping of the brain]. / Obnaruzhenie aktivatsii motornoi kory koshki pri dvizhenii konechnosti s pomoshch'iu termokartirovaniia mozga.

In chronic experiments on cats the distribution of temperature on the dorsal surface of the cerebral cortex and its dynamics were studied through unopened skull by the thermovision and digital image processing technique. During the reflex movement of the forelimb and after it focal biphasic thermoreactions in the motor cortex which lasted for up to 30 s and sign-opposite thermoreactions in symmetrical points of both hemispheres were revealed.

[Movement of temperature waves across the cerebral cortex of the white rat]. / Dvizhenie termovoln po kore mozga beloi krysy.

In acute experiments on immobilized or anesthetized white rats the spatial distribution and dynamics of temperature on the dorsal surface of the cerebral cortex were investigated by the thermovision technique and digital image processing through the intact skull. Under certain conditions the appearance of moving thermowaves that spread over the cortex for 8-30 mm during 2-9 s with a rate of 2-10 mm/s was found. Among the trajectories of these waves the circular one was more common: it began in one hemisphere, spread in one or another direction, then went over to the second hemisphere, moved in the opposite direction and came back to the initial zone. Linear and semicircular trajectories were found as well with or without crossing from one hemisphere to the other. The mechanisms and possible functional significance of the effect are discussed.

[Parameters of photic stimulation and characteristics of thermoreactions in the cerebral cortex of the white rat]. / Parametry svetovoi stimuliatsii i kharakteristiki termoreaktsii v kore golovnogo mozga beloi krysy.

The dynamics of local thermoresponses in the brain cortex was studied through the unopened scull under patterned light stimulation of the retina in acute experiments on white rats by means of thermovision and digital image processing technique. The dependence of the amplitude, temporal and spatial characteristics of these responses on the size, retinal localization, focusing of the stimulus, its duration, number and frequency of presentation was estimated. The properties, significance and mechanisms of the revealed thermoeffects are discussed.

[Sensory mapping of the rat cerebral cortex by thermographic methods]. / Sensornoe kartirovanie kory mozga krysy metodami termovideniia.

Using thermovision and digital image processing, the dynamics of thermomap in the brain cortex has been studied on albino rats through the opened skull before and during sensory stimulation. Photic, sonic and somatosensory stimuli lead to the onset of local heating foci in the corresponding cortical zones, as well as to local multiple thermoresponses in other areas. Some quantitative parameters of these effects are given and their possible mechanisms are discussed.