Stimulus Specific Adaptation And Regularity In The Medial Geniculate Body

Detecting the rule of external stimuli is essential for animal survival.The auditory system has different mechanisms for short-term and long-term rule detection,corresponding to stimulus-specific adaptation(SSA)and regularity sensitivity(Regularity).SSA refers to neurons showing a stronger response to deviant stimuli compared to the repetitive stimuli,and Regularity refers to the sensitivity of neurons to stimuli combination in the long-term temporal structure.SSA has been extensively investigated in the entire auditory pathway from the cochlear nucleus to the auditory cortex(AC).In the lemniscal pathway,people think SSA began to emerge in the primary auditory cortex(A1).However,most of these researches were conducted with the neuronal characteristic frequency(CF),and there was no information regarding whether SSA was frequency-dependent;therefore,SSA in A1 may also originate from the auditory thalamus(MGB)through the non-CF frequency band.Previous researches into Regularity were only focused on AC,but whether Regularity in AC originated from MGB is still lacking related research,and the relationship between SSA and Regularity was seldom explored.In this dissertation,we investigated MGB with the following three aims:(1)the frequent dependence of SSA;(2)the Regularity in MGB;(3)the relationship between SSA and Regularity.In this dissertation,extracellular electrophysiological techniques were employed to record MGB neurons’s spike in anesthetized rats.The frequent dependence of SSA was investigated through our systematically changing the frequency in oddball stimulation;we explored the Regularity in MGB by comparing the response of regular and irregular oddball stimulation and discussed the relationship between SSA and Regularity.Here are the results:(1)When the frequency of oddball stimulation deviated from the CF of the neuron,neurons in different subregions of MGB exhibited a stronger SSA;thus,SSA in MGB is frequency-dependent.Meanwhile,neurons in the ventral region of MGB also showed significant SSA in the non-CF band,suggesting that the SSA in Al may originate from MGB.(2)The responses of MGB to deviant and standard stimuli were similar in the regular and irregular oddball stimulation respectively,suggesting that the Regularity in MGB was very weak relative to that in AC.With different frequency bands,no significant difference was detected in Regularity,indicating that Regularity did not depend on frequency.These results suggested that the Regularity in the auditory system may originate from AC.(3)The strength of SSA in the regular and irregular oddball stimulation was strongly correlated,and the former was significantly larger than the latter.It shows that there is an interaction between SSA and Regularity,and Regularity may promote SSA.Our results indicated that SSA and Regularity were not completely separated but somehow connected in their neural mechanisms.In summary,our results showed that MGB neurons were capable of change detection from the background,but were not sensitive to the sound combination,which provided new evidence for the origin in representation of short-term and long-term rule detection in the auditory system.