Abstract
The response of neurons in the Red Nucleus pars magnocellularis (RNm) to both tone bursts and electrical stimulation were observed in three cynomolgus monkeys (Macaca fascicularis), in a series of studies primarily designed to characterize the influence of the dopaminergic ventral midbrain on auditory processing. Compared to its role in motor behavior, little is known about the sensory response properties of neurons in the red nucleus (RN); particularly those concerning the auditory modality. Sites in the RN were recognized by observing electrically evoked body movements characteristic for this deep brain structure. In this study we applied brief monopolar electrical stimulation to 118 deep brain sites at a maximum intensity of 200 μA, thus evoking minimal body movements. Auditory sensitivity of RN neurons was analyzed more thoroughly at 15 sites, with the majority exhibiting broad tuning curves and phase locking up to 1.03 kHz. Since the RN appears to receive inputs from a very early stage of the ascending auditory system, our results suggest that sounds can modify the motor control exerted by this brain nucleus. At selected locations, we also tested for the presence of functional connections between the RN and the auditory cortex by inserting additional microelectrodes into the auditory cortex and investigating how action potentials and local field potentials (LFPs) were affected by electrical stimulation of the RN.
Highlights
The Red Nucleus (RN) or nucleus ruber lies in the rostral midbrain and derives its name from the high concentration of ironcontaining pigments within its cellular structure (Hernandez, 1931)
The response of neurons in the Red Nucleus pars magnocellularis (RNm) to both tone bursts and electrical stimulation were observed in three cynomolgus monkeys (Macaca fascicularis), in a series of studies primarily designed to characterize the influence of the dopaminergic ventral midbrain on auditory processing
Since the red nucleus (RN) appears to receive inputs from a very early stage of the ascending auditory system, our results suggest that sounds can modify the motor control exerted by this brain nucleus
Summary
The Red Nucleus (RN) or nucleus ruber lies in the rostral midbrain and derives its name from the high concentration of ironcontaining pigments within its cellular structure (Hernandez, 1931). Compared to its role in motor behavior little is known about sensory response properties of neurons in the RN, those concerning the auditory modality. Neurons in the rostral RN have been found to exhibit short-latency responses to clicks and tones (Massion and Albe-Fessard, 1963; Irvine, 1980). Bratus et al (1981) recorded evoked potentials from the magnocellular RN in anesthetized cats, and showed that the response latency varies from 3.5 to 10.5 ms, depending on the intensity of the auditory stimulation. It has been hypothesized that the RN is a component of the subcortical path for reflexes connected with turning the ear in the direction of sound (Courville, 1968), and that it is a part of the complex pathways concerned with the animal’s postural and defensive responses to acoustic stimulation (Martin and Dom, 1970)
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