Orbitofrontal Cortex: Modeling Prefrontal Function in Rats

2 a common functional identity is determined by the same type of structure and connections, whatever the mammal examined. … stratiographic analogy, grossly appreciated in Nissl or Weigert preparations, constitutes a valuable data point, but it is not completely decisive or infallible. – Cajal (1988, p 524). Introduction In histological preparations, a signature granular cell layer distinguishes a broad expanse of prefrontal cortex positioned rostral to motor cortex in both human and nonhuman primate brains. While cytoarchitectonic criteria originally provided a basis for defining cortical areas (Brodmann 1909), it was recognized in early writings that 'functional identity' of structures between different species would ultimately depend on data, then largely unavailable, regarding specific anatomical connections and physiology rather than 'stratiographic analogy' (Cajal, 1988). Since the middle of the last century the definition of prefrontal cortex has been influenced by a wealth of new information on neuroanatomical connections gained from tract tracing studies (see Preuss, 1995 for review). As Cajal envisioned, these new data indicate that prefrontal areas share functions in different species even in the absence of a granular cell layer. Early on, Rose and Woolsey (1949) proposed that projections from mediodorsal (MD) thalamus defined prefrontal cortex. Indeed, the cytoarchitectonic definition of prefrontal cortex in the nonhuman primate corresponded well with the topography of innervation from MD. Since then it has become clear that an additional defining feature of prefrontal cortex is its rich interconnections with other brain systems, including other " association " areas of posterior and temporal neocortex, limbic structures such as the hippocampus and amygdala, and major efferent provided an important basis for further subdividing regions of prefrontal cortex and guiding functional analysis of prefrontal systems. The prefrontal cortex in the primate, which constitutes nearly a third of the neocortex, is now widely recognized to comprise three main subdivisions: a orbitofrontal division of prefrontal cortex, providing an overview of recent research that suggests strong functional homologies between orbitofrontal cortex in primate brain and a region in the rat brain that shares similar anatomical connectivity. In the rat, mediodorsal thalamus can be divided into three segments (Krettek and Price, 1977a; Groenewegen, 1988). Projections from the medial and central segments of MD define a region that includes orbital areas and the ventral and dorsal agranular insular cortices (Leonard, These regions of MD in rat receive direct afferents from amygdala, medial temporal lobe, and the ventral pallidum/ventral tegmental area; and olfactory …