Omission responses in human inferior colliculus and medial geniculate body

Predictive coding postulates that our brain develop an internal model of the external world to predict incoming information. However, these internal models need to be constantly updated, since the expected stimulus and actual sensory input could not coincide. This discrepancy generates activations in the brain, the so-called prediction errors. There are two types of prediction errors: the positive prediction error is triggered when an unpredicted stimulus appears, whilst negative prediction error is triggered by the omission of a predicted stimulus. This fMRI study explores the involvement of auditory subcortical nuclei, specifically the inferior colliculus (IC) and the medial geniculate body (MGB), in eliciting and encoding negative prediction errors. Five healthy participants were involved in the study, employing a variation of the auditory oddball paradigm with abstract rules to manipulate subjects’ expectations. Notably, subjects were aware that within a 7-sound sequence, one...Show morePredictive coding postulates that our brain develop an internal model of the external world to predict incoming information. However, these internal models need to be constantly updated, since the expected stimulus and actual sensory input could not coincide. This discrepancy generates activations in the brain, the so-called prediction errors. There are two types of prediction errors: the positive prediction error is triggered when an unpredicted stimulus appears, whilst negative prediction error is triggered by the omission of a predicted stimulus. This fMRI study explores the involvement of auditory subcortical nuclei, specifically the inferior colliculus (IC) and the medial geniculate body (MGB), in eliciting and encoding negative prediction errors. Five healthy participants were involved in the study, employing a variation of the auditory oddball paradigm with abstract rules to manipulate subjects’ expectations. Notably, subjects were aware that within a 7-sound sequence, one sound would be omitted in one of three known positions. We conducted a two-level analysis: the first level used a General Linear Model (GLM) on single subjects, followed by a second analysis using a Linear Mixed Effect (LME) model at the group level. Both bilateral MGB and left IC showed activations in response to omitted sounds. Notably, only the bilateral MGB resulted in encoding negative prediction errors, showing a decreased activation as subjects’ expectations of sound omissions increased. Our findings suggest that the auditory brain dynamically updates the internal model of the external environment when the sensory input deviates from expectations, such as the omission of expected sounds. The results provide insights into the hierarchical organisation of the auditory pathway, paving the way for future research to explore the differential involvement of auditory lemniscal and non-lemniscal pathways in encoding negative prediction errors. Additionally, this study posits the first steps in comprehending the neural processes underlying auditory perception as well as in providing insights for understanding perceptual anomalies, such as hallucinations and delusions.Show less

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Omission responses in human inferior colliculus and medial geniculate body