Cognitive impairments after lesions of the neostriatum caudolaterale and its thalamic afferent in pigeons: functional similarities to the mammalian prefrontal system?

Several studies suggest that the neostriatum caudolaterale (NCL) of birds is equivalent to the mammalian prefrontal cortex (PFC). The aim of the present study was to analyze the functional importance of the NCL and the n. dorsolateralis posterior thalami (DLP), the main thalamic afferent structure of the NCL, in tasks which are generally used to assess mammalian prefrontal functions. The DLP is, due to its subtelencephalic connectivities, different from the mammalian n. mediodorsalis (MD), the thalamic afferent nucleus of the PFC. However, it is possible that in its interactions with the forebrain the DLP subserves similar functions as the mammalian MD. Pigeons with lesions of the NCL, the DLP or, as a thalamic control, the n. geniculatus lateralis, pars dorsalis (GLd) were tested in a delayed alternation and in a go/no-go task. The results demonstrate that NCL-lesioned birds are impaired in both tasks, while DLP-lesioned animals display deficits only in the delayed alternation experiment. The performance of the GLd-lesioned pigeons was not attenuated in either task. It is concluded that the functional similarities of the prefrontal cortex and the NCL extent at least partly to their thalamic afferent structures, although these diencephalic nuclei differ considerably in their anatomy.