Experimental-design Specific Changes in Spontaneous EEG and During Intermittent Photic Stimulation by High Definition Transcranial Direct Current Stimulation.

Electroencephalography (EEG) as a biomarker of neuromodulation by High Definition transcranial Direct Current Stimulation (HD-tDCS) offers promise as both techniques are deployable and can be integrated into a single head-gear. The present research addresses experimental design for separating focal EEG effect of HD-tDCS in the '4-cathode × 1-anode' (4 × 1) montage over the left motor area (C3). We assessed change in offline EEG at the homologous central (C3, C4), and occipital (O1, O2) locations. Interhemispheric asymmetry was accessed for background EEG at standard frequency bands; and for the intermittent photic stimulation (IPS). EEG was compared post- vs pre-intervention in three HD-tDCS arms: Active (2 mA), Sham (ramp up/down at the start and end), and No-Stimulation (device was not powered), each intervention lasting 20 min. The asymmetric background EEG changes were only in the central areas with right-side amplitude spectra prevalence, most pronounced in the no-stimulation arm, where they depended on comparison time-points and were consistent with markers of transition between drowsiness and vigilance - bilateral decrease in the delta and asymmetric central increase in the alpha and beta1 bands. For the active arm, similar but less pronounced changes occurred in the alpha band. In contrast, responses to IPS developed similar asymmetric amplitude increase at four harmonics of the IPS of 3 Hz only in the active arm, against a background of a brain-wide symmetric increase in both active and sham arms. Our protocols and analyses suggest methodological caveats for how EEG of tDCS studies could be conducted to isolate putative brain polarization outcomes.

Morphological brain asymmetries in male mice with callosal defects due to prenatal gamma irradiation.

We have previously suggested a relationship between the development of the corpus callosum and the direction of cerebral asymmetries (Schmidt and Caparelli-Daquer, 1989; Schmidt et al., 1991). Here we report a study on morphological brain asymmetries using a distinct experimental approach. At embryonic day 16, mice were exposed to a gamma source, receiving a total dose of 2 Gy. At adulthood 32 irradiated and 28 normal male Swiss mice were evaluated for individual and populational interhemispheric asymmetries of weight, dorsal area, and neocortical volume. All irradiated mice showed callosal defects ranging from total absence to a partial reduction of the midsagittal callosal area. The normal and irradiated groups displayed a pronounced individual asymmetry in all measurements. In contrast, populational asymmetry could be identified only in the normal group. These results are consistent with our previous data in acallosal mutant mice and support the hypothesis that the corpus callosum may play a role in directing interhemispheric morphological brain asymmetries.

Absence of population cerebral asymmetries in mice with callosal defects induced by prenatal gamma irradiation.

The development of the corpus callosum of 19 male Swiss mice was disturbed by exposure to a 60Co gamma source on embryonic day 16 with a total dose of 2 Gy (dose rate of 56 to 59 rads/min). At adulthood the animals were perfused with saline followed by formaldehyde and the cerebral hemispheres were weighed and photographed in dorsal, lateral and medial views. Brain asymmetries were evaluated by measurements of hemisphere weight, as well as dorsal and lateral areas. From the measurements of the midsagittal callosal areas, performed on the medial views, 2 subgroups could be identified: one with a small callosal remnant (N = 9) and another with a non-measurable callosal area (N = 10). In spite of a pronounced individual asymmetry, the irradiated mice (N = 19) did not show a populational asymmetry toward any side. A slight tendency favoring the left hemisphere was found in the small remnant subgroup. These results are consistent with our previous data for a strain of mice in which some animals present callosal defects. We conclude that the present data support the hypothesis that the corpus callosum may play a role in directing morphological hemispheric asymmetries.

Paw preference in mice with callosal defects induced by prenatal gamma irradiation.

The development of the corpus callosum of male Swiss mice was perturbed by exposure to gamma radiation at embryonic day 16 with total doses of 2 Gy (N = 48) or 3 Gy (N = 26). At adulthood paw preference was studied in these callosal defective animals and in 93 control nonirradiated male Swiss mice. The analysis of directional laterality indicated a populational tendency for right paw use in the 2 Gy group (60%) that was markedly increased in the 3 Gy group (95%). In the 3 Gy group, directional laterality was significantly different from chance in contrast to that observed in normal controls (49%). In the three groups most mice presented a significant individual paw preference. These data are consistent with our hypothesis that the early absence of the corpus callosum disrupts the normal pattern of directional asymmetries.

The effects of total and partial callosal agenesis on the development of morphological brain asymmetries in the BALB/cCF mouse.

The corpus callosum fails to develop in some mice of the BALB/cCF strain. We report here a study on cerebral morphological asymmetry in males of this particular strain in order to test the hypothesis that the normal development of the corpus callosum is responsible for the establishment of brain asymmetries. In 46 animals the dorsal area and the weight of each hemisphere were measured. In order to identify the animals with callosal defects and check for size anomalies of the anterior commissure, the hemispheres were cut into sagittal sections and stained with cresyl violet. Measures of sagittal area of the anterior commissure did not support the hypothesis that this commissure is enlarged when the corpus callosum is reduced or absent. In normal animals, the mean difference between left and right dorsal cortical areas showed a significant directional asymmetry, the left being consistently greater than the right. A similar pattern was found for weight. In mice with callosal defects there were no significant differences, either between the dorsal areas or between the weights of the hemispheres. However, data on the absolute values of the hemispheric differences indicated the presence of a nondirectional asymmetry not only in normal animals, but also in mice with callosal defects. Therefore, our data suggest that the ontogenesis of the corpus callosum plays a role in directing the development of cerebral asymmetries.

Contralateral rotatory bias in the free-swimming test after unilateral hemispherectomy in adult Swiss mice.

In the free-swimming rotatory test mice spend most of the time swimming close to the wall of the container attempting to escape from an aversive test situation. The attraction to the wall may suggest that turning behavior in the free-swimming test reflects the existence of intrinsic sensory asymmetries, which determine preferential attention adhesion to one side. In order to test this hypothesis, we investigated the rotatory swimming behavior of mice submitted to a unilateral hemispherectomy at adulthood, a condition of extreme sensory asymmetry. Fifteen days after surgery procedures, each mouse was tested for 5 min on 3 different days. We found that the hemispherectomized mice had a significant strong bias to turn in the direction contralateral to their lesion. These data could be explained considering that, in attempting to escape from the test situation, animals bring the recipient wall into their intact sensory field and, as a consequence, set the direction of locomotion. Thus, the free-swimming test may be useful to investigate sensory asymmetries during an aversive test situation.

Paw preference in mice with callosal defects induced by prenatal gamma irradiation

The development of the corpus callosum of male Swiss mice was perturbed by exposure to gamma radiation at embryonic day 16 with total doses of 2 Gy (N = 48) or 3 Gy (N = 26). At adulthood paw preference was studied in these callosal defective animals and in 93 control nonirradiated male Swiss mice. The analysis of directional laterality indicated a populational tendency for right paw use in the 2 Gy group (60 per cent ) that was markedly increased in the 3 Gy group (95 per cent ). In the 3 Gy group, directional laterality was significantly different from chance in contrast to that observed in normal controls (49 per cent ). In the three groups most mice presented a significant individual paw preference. These data are consistent with our hypothesis that the early absence of the corpus callosum disrupts the normal pattern of directional asymmetries

Absence of populational cerebral asymmetries in mice with callosal defects induced by prenatal gamma irradiation

The development of the corpus callosum of 19 male Swiss mice was disturved by exposure to a 60Co gamma source on embryonic day 16 with a total dose of 2 Gy (dose rate of 56 to 59 rads/min). At adulthood the animals were perfused with saline followed by formaldehyde and the cerebral hemispheres were weighed and phtographed in dorsal, lateral and medial views. Brain asymmetries were evaluated by measurements of hemisphere weight, as well as dorsal and lateral areas. From the measurements of the midsagittal callosal areas, performed on the medial views, 2 subgroups could be identified: one with a small callosal remnant (N=9) and another with a non-measurable callosal area (N=10). In spite of a pronounced individual asymmetry, the irradiated mice (N=19) did not show a populational asymmetry toward any side. A slight tendency favoring the left hemisphere was found in the small remmant subgroup. These results are consistent with our previous data for a strain of mice in which some animals present callosal defects. We conclude that the present data support the hypothesis that the corpus callosum may play a role in directing morphological hemispheric asymmetries