Sensory prediction or timing? : clarifying cerebellar function by examining the mismatch negativity in patients with cerebellar degeneration

Abstract

Abstract Background and aim: Over the last few decades increasing evidence suggests that the functional domain of the cerebellum extends beyond motor control. Two functional hypotheses attempting to account for cerebellar involvement also in a range of perceptual and cognitive tasks are the sensory prediction hypothesis and the timing hypothesis. The sensory prediction hypothesis postulates that the cerebellum is critical in generating expectancies regarding forthcoming sensory information. The timing hypothesis postulates that this structure is critical for the learning and retention of temporal information, a more limited, yet specific form of prediction. Recent functional imaging and patient studies have produced evidence compatible with both of these positions. The aim of the present experiment was to contrast these two hypotheses by examining the mismatch negativity (MMN) response in patients with cerebellar cortical atrophy. While the timing hypothesis would predict a selective impairment in the MMN response to the deviants of a longer duration than the standard, the sensory prediction hypothesis would also predict similar impairments in the MMN response to deviants of higher pitch, lower intensity and a different spatial location. Method: Patients and matched controls were presented with a stream of short sounds while watching a silent movie. A standard auditory stimulus was presented 60% of the time, composed of a fixed duration, intensity, and pitch, and presented at a fixed location. The remaining sounds deviated on one of these four dimensions (10 % each). Key result: Compared to controls, the patients exhibited delayed duration MMN latency, as well as a similar trend for the intensity MMN. The pitch and location MMNs did not differ between patients and controls. Conclusion: The present results fail to support a more general role in sensory prediction as predicted by the sensory prediction hypothesis, while the timing hypothesis receives partial support. Importantly, the present findings add to previous reports of timing deficits in cerebellar patients by demonstrating that this impairment is present at an early stage of auditory processing (100-200 ms), even when the task does not require an overt assessment of temporal regularities or even that the stimuli be attended.