Table 2.
Etiologies and brain mechanism proposed for ASD and its coincidence with SC compromise (see text for references).
| Etiologies or brain mechanism of ASD | SC functions |
|---|---|
| Genetic markers of ASD are related to synaptic formation, cell adhesion molecules, axon guidance, etc. | The SC is the main brain organizer (by early visual input) during the first months of life. Several specific genes related with retino-tectal axon guidance and cortical-SC connections are related with ASD etiology. |
| GABA is the main synaptogenic neurotransmitter during early life. | The SC is the main GABAergic brain center with a generalized influence on sensitive, motor and emotional circuits. |
| Fetal valproate syndrome | Specific compromise of gabaergic SC’ neurons in rats exposed to the valproic acid: they showed difficulties in social and exploratory behavior, abnormal sensory patterns and diminished prepulse inhibition (PPI). |
| Others neurotransmitters and hormones (OXT, testosterone, dopamine, glutamate, nitric oxide, choline, etc.) have been implicated in the pathogenesis of ASD. | Most reward related dopaminergic circuits are activated by the SC. The interaction between OXT and testosterone has an influence on the gaze behavior toward faces (aversion or indifference)∗ which are closely related with the SC. Most neurotransmitters and neurotrophic factors have input and/or output influence on the SC. |
| Impaired gamma band synchrony in ASD. | Widespread cortical synchronized gamma band activity is triggered by SC activation. |
| New images studies found selective long range cortico-cortical hypoconnectivity in areas related to the social brain, and hyperconnectivity in subcortical thalamic structures. | The SC could be responsible of the hypoconnectivity of the social brain network regarding its specific role on these brain areas during early human development. The recent finding of subcortical hyperconnectivity reinforces the theory of subcortical network compromise (whose center is the SC) and explains several symptoms such as the stereotypies, the abnormal PPI, obsessions, etc. |
| Prenatal neuroinflammation is a proposed etiology of ASD. | Impaired social behavior by compromise of the optic tectum was observed in tadpoles exposed to elevated levels of pro-inflammatory cytokines (PIC) during early development. |