Recent Advances in Human Neurophysiology.
March 1998. Okazaki, Japan.
Comparative Analysis using VEPs showed many abnormalities in autistic respect to healthy children.
Recent Advances in Human Neurophysiology.
March 1998. Okazaki, Japan.
AGUILAR L. C., MARTIN R., CRUZ S., ROSIQUE P., ISLAS A.AND ALFAROF.
Instituto de Investigaciones en Neuroplasticidad y Desarrollo Celular. Departamento de Biologia Celular y Molecular de la Universidad de Guadalajara. Guadalajara, Jalisco MEXICO.
INTRODUCTION
The knowledge about the neural sources of some components of the flash VEPs and the normal sequence of these components is limited. Anatomical and physiological studies has shown visual projections to areas outside the occipital lobe (Von Essen 1979, Kuypers et al. 1965, Bignall and Imbert 1969, Boyd et al. 1971) indicating cortico-cortical connections from visual association areas to parietal lobe, premotor, prefrontal cortex and to middle and inferior temporal gyri. Recordings in humans (Walter and Walter 1949; Brazier 1964) have shown VEPs in frontal and temporal regions. Studies performed by Hammond et al. 1989, showed that the topographic flash VEPs can provide data on the location of lesions remote from the occipital area, where usually the components were asymmetrical, caused by a depression or enhancement of some component. In other hand the flash VEPs are in many cases of children with mental retardation and autism, the only possibility to perform a visual evoked potential study, for there is not patient collaboration for performing the study which has to be performed in sleep stage. We performed a prospective topographic flash VEPs study in normal and autistic children in order to know the normal sequence of components, the grade of interhemispheric symmetry for each area and the comparison with autistic children.
METHODS
Topographic flash VEPs were recorded from a control group (n=40) and from autistic patients (DSM IV, n=103), both sexes, between 3 and 13 years. The stimulation was performed using a white stroboscopic xenon flash (Grass PS22). All stimuli were presented binocularly with a variable repetition rate during sleep (stage II), 16 electrodes were placed according to 10-20 international system, amplifier bandpass filters 1-35 Hz, 200 epochs were averaged and obtained twice. Symmetry analysis of each area was performed using Pearson Coefficient (PC) to know the linear correlation and energy ratio (ER) to know the symmetry in area below the curve, for 50-200 and 200-400 milliseconds (ms) segments, the result of each area on a specific segment of time of every autistic child was compared with a control group using Z transform (p<0.025) for knowing the significant deviations.
RESULTS
The following sequence of negative components was observed in normal controls: The initial response was detected in frontopolar regions (FP1-FP2), followed by occipitals (O1-O2), continuing with parietals (P3-P4), then temporals (T5-T6), followed by frontopolars, frontals (F3-F4), centrals (C3-C4), followed by occipitals, parietals and temporals (Fig.1 and 2). The linear correlation analysis showed high symmetry with a values higher to 0.70 (Pearson coefficient) for p<0.025. The symmetry analysis of ABC studied through ER showed in control group values of one side respect to contra lateral no higher than 2.5 times and no lower than 0.4 times., this for a P<0.025 (Fig. 1 and 2), only the frontopolars (Fp1-Fp2) in the 50-200 ms segment, the frontolaterals (F7-F8) and anterior temporals (T3-T4) showed low symmetry in this parameters, observing a grate dispersion in the values of these regions.
|
Fig. 1.- Flash VEPs of a control child, female 12 years old. Notice the sequence of negative components and the high symmetry in linear correlation and area below the curve studied by energy ratio
|
Fig. 2.- Flash VEPs of a 6 month old male. Observe the high symmetry quantified by Pearson coefficient (PC) (Linear correlation) and energy ratio (ER), only the T3-T4 and F7-F8 and FP1-FP2 in 50-200 ms segment showed low PC and ER. |
In autistic children the sequence of components showed many abnormalities including depression, enhanced of components, like to previous observations in patients with brain damage reported by Hammond et al 1989 (Fig. 3 and 4), or premature apparition of a specific component like the negative component (NC) in parietal (Fig. 4) that usually appears after the occipital N100 (Fig. 1 and 2) in controls, this abnormalities were observed mainly in right posterior regions ; the reduction of voltage (mainly in P4,T6 and O2) was mostly seen (Fig. 3). The symmetry analysis shows many deficiencies in linear correlation where parietals (P3-P4) presented significant low PC (p<0.025) in 63% of patients and 66 % in T5-T6 for the 200-400 ms segment.
Also the autistic group showed significant asymmetries of ER (p<0.025) in 56% of the patients in P3-P4, 40 % in O1-O2 and 39 % in T5-T6 for the 200-400 ms segment.
|
Fig. 3.- Flash VEPs of autistic child, 6 year old male. Notice the great reduction of voltage in 02, T6 and P4, and the very low Pearson coefficient in the mentioned areas |
Fig. 4.- Observe the premature response of negative component in P4, which appear prior to N100 in O2, also the Pearson coefficient and energy ratio are very low in P3-P4 and T5-T6. |
DISCUSSION AND CONCLUSIONS
The mentioned results indicate that there is a normal sequence of responses after a flash stimulation that can be reflecting the cognitive process. The symmetry analysis in the control healthy group showed that the high symmetry observed in frontal, central, parietal, occipital and temporal posterior regions was no age-dependent, this symmetry was high including in a 6 month old normal child (Fig. 2). The study of mentioned sequence in autistic children and the symmetry analysis through PC and ER that contributed greatly to perform a more objective and reliable study, indicated that parietal and temporal regions are frequently affected in autism, only 2 autistic children of 103 did not show some abnormality of Flash VEPs in this areas, but one of them showed in the EEG spikes in both temporal lobes (T3 and T4) and the second one showed spikes in frontal regions and seizures every week. These results strongly suggest that the parietal and temporal regions are affected in autistic children and according to Hammond et al. 1989, these asymmetries can be reflecting lesion or damage.
The neuropsychological analysis performed in the autistic group showed that the language and visual motor skills were the most deficient functions. This functions are related with temporal (Mc Carthy and Warrington 1990) and parietal ( Perenin and Vighetto, 1988) regions. We conclude that parietal and temporal regions are high frequently affected in autism.
REFERENCES
Von Essen DC. 1979. Visual areas of the mammalian cerebral cortex. Annu Rev Neurosci. 2:227-263.
Kuypers HGJM. Szwarcbart MK. Mishkin M. Rosvold HE. 1965. Occipitotemporal corticocortical connections in the rhesus monkey. Exp Neurol. 11: 245-262.
Bignall KE. Imbert M. 1969. Polisensory and corticocortical projections to frontal lobe of squirrel and rhesus monkeys. Electroencephallogr Clin Neurophysiol 26: 206-215.
Boyd EH. Pandya DN. Bignall KE. 1971. Homotopic and nonhomotopic interhemispheric cortical projections in the squirrel monkey. Exp Neurol. 32: 256-274
Walter VJ and Walter WG. 1949. The central effects of rythmic sensory stimulation. Electroencephalogr Clin Neurophysiol. 1: 57-86.
Brazier MAB. 1964. Evoked responses recorded from the depths of human brain. Ann NY Acad Sci. 112: 33-59.
Hammond EJ. Barber CP. Wilder BJ. 1989. Flash Visual Evoked Potential Topographic Mapping: Normative and Clinical Data. In: Topographic Brain Mapping of EEG and Evoked Potentials. (Maurer K Ed) Springer-Verlag.
McCarthy R. Warrintong EK. 1990. Cognitive Neuropsychology. A clinical Introduction. Academic Press.
Perenin MT. Vighetto A. 1988. Optic Ataxia a specific disruption in visomotor mechanism. Brain. 111: 643-674.
Comentarios