The cochlear nucleus (CN), as the first brain centre in the auditory system is responsible for sorting the neural signals received from the cochlea, into parallel processing streams for transmission to the assorted higher auditory nuclei. A commissural connection formed between cochlear nuclei through direct projections, thereby provides the first site in the central auditory system at which binaural information is able to influence the ascending auditory signal. This thesis investigates the nature of commissural projections and the impact of their input upon neurons of the ventral CN (VCN) through in vivo intracellular and extracellular electrophysiological recordings together with both acoustic and electrical stimulation of the contralateral CN.

The present thesis examined the behavioural and brain mechanisms of associative change in the rat during Pavlovian fear conditioning as measured by freezing. The first series of experiments (Chapter 3) used compound test designs to study how learning is distributed among excitatory and neutral conditional stimuli (CSs). More was learned about a neutral CSB than an excitatory CSA when trained in isolation, indicating that fear learning is negatively accelerated. CSA blocked fear learning to CSB when trained in compound. Unblocking of CSB occurred if the AB compound signalled an increase in unconditional stimulus (US) intensity or number. Assessments of associative change during blocking showed that more was learned about CSB than CSA. Such assessments during unblocking revealed that more was learned about CSB than CSA following an increase in US intensity but not US number. These US manipulations had no differential effects on single-cue learning. The results show that variations in US intensity or number produce unblocking of fear learning, but for each there is a different profile of associative change and a potentially different mechanism. The second series of experiments (Chapter 4) demonstrated that these stimulus selection effects are mediated, at least in part, by nucleus accumbens shell (AcbSh). AcbSh lesions augmented overshadowing during compound conditioning and promoted learning about CSA at the expense of CSB during blocking designs. Lesioned rats could learn normally about the novel CSB if it was rendered more informative regarding shock in Stage II. These results identify an important role for AcbSh and ventral striatum in distributing attention and learning among competing predictors of danger.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 59-64).

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 132-143).

Zugl.: Berlin, Charité, University-Med., Diss., 2006.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Dissertation (Ph.D.) -- University of Texas Southwestern Medical Center at Dallas, 2008. / Vita. Bibliography: p.104-121

Thesis (Ph. D.)--University of Washington, 2008. / Vita. Includes bibliographical references (leaves 105-114).

Zugl.: Rostock, Univ., Diss., 2007

Mémoire (M.Eng.)--Université du Québec à Chicoutimi, 1995. / Document électronique également accessible en format PDF. CaQCU