The Nuclei of the Lateral Lemniscus
Parallel processing streams guide ascending auditory information through the processing hierarchy of the auditory brainstem. Many of these processing streams converge in the lateral lemnisucus, the fiber bundle that connects the cochlear nuclei and superior olivary complex with the inferior colliculus. The neuronal populations within the lateral lemniscus can be segregated according to their gross structure-function relationships into three distinct nuclei. These nuclei are termed ventral, intermedial, and dorsal nucleus, according to their position within the lemniscal fiber bundle. The complexity of their input pattern increases in an ascending fashion. The three nuclei employ different neurotransmitters and exhibit distinct synaptic and biophysical features. Yet they all share a large heterogeneity. Functionally, the ventral nucleus of the lateral lemniscus has been hypothesized to reduce spectral splatter by generating a rapid, temporally precise feedforward onset inhibition in the inferior colliculus. In the intermedial nucleus of the lateral lemniscus a cross-frequency integration has been observed. The hallmark of the dorsal nucleus of the lateral lemniscus is the generation of a long-lasting inhibition in its contralateral counterpart and the inferior colliculus. This inhibition is proposed to generate a suppression of sound sources during reverberations and could act as a temporal filter capable of removing spurious interaural time differences. While great advances have been made in understanding the role that these nuclei play in auditory processing, the functional diversity of the individual neuronal responsiveness within each nucleus remains largely unsolved.