This study investigated differentiation of Macaca fuscata auditory thalamus into chemically defined nuclei forming relays to auditory cortical areas. The thalamus was stained immunocytochemically for parvalbumin and 28 kDa calbindin in normals and in brains in which retrogradely transported tracers were injected into middle layers of auditory cortical areas or applied to the cortical surface. Parvalbumin- and calbindin-immunoreactive cells show a complementary distribution in ventral, anterodorsal, posterodorsal, and magnocellular medial geniculate nuclei. The ventral nucleus has a high density of parvalbumin cells and few calbindin cells, and the anterodorsal nucleus has a high density of parvalbumin cells and moderate numbers of calbindin cells. Both nuclei have a dense parvalbumin-immunoreactive neuropil formed by terminations of fibers ascending in the brachium of the inferior colliculus. The posterodorsal nucleus has approximately equal proportions of parvalbumin and calbindin cells; neuropil staining is weak but contains terminations of calbindin-immunoreactive fibers ascending in the midbrain tegmentum. The magnocellular nucleus contains domains of parvalbumin and calbindin cells. Parvalbumin cells in the ventral nucleus project to a central core of auditory cortex with densest parvalbumin immunoreactivity. Those in anterodorsal and posterodorsal nuclei project to surrounding auditory fields with less dense parvalbumin immunoreactivity; those in the magnocellular nucleus project widely to auditory and other fields. Injections of middle cortical layers label a large majority of parvalbumin cells in the ventral, anterodorsal, or posterodorsal nuclei and in the magnocellular nucleus. Superficial deposits label calbindin cells only, usually in more than one nucleus, implying a widespread projection system.

The aim of this investigation was to characterize auditory areas of the primate cerebral cortex on the basis of chemoarchitecture. Cortical areas of the supratemporal plane were delineated in Macaca fuscata (M. fuscata) by immunocytochemical staining for parvalbumin, staining for cytochrome oxidase, examination of cyto- and myeloarchitecture, and retrograde tracing of corticocortical connections. Comparative observations were made on Macaca fascicularis (M. fascicularis). Differential staining of fiber plexuses, probably of thalamic origin, identifies a central core zone of dense immunostaining and a surrounding zone of moderate-to-dense immunostaining composed of anteromedial, lateral, and posteromedial fields. Outside the second zone, there is a third anterolateral zone of weaker immunoreactivity, and, outside that zone, there is a fourth zone in which immunoreactivity is virtually absent. Differences in parvalbumin immunostaining in the auditory fields may reflect differences in relative contributions of thalamic inputs from parvalbumin-immunoreactive cells in the medial geniculate complex. The central core zone and the surrounding three fields can be correlated with major auditory fields previously defined by multiunit mapping and thalamocortical connectivity. The core zone contains a large principal field and an anterior extension. The pattern of corticocortical connections between these and adjoining fields suggests that the anteromedial, lateral, and posteromedial fields represent first steps in three streams of connections passing outward from auditory into association cortex. M. fuscata has an unusually large auditory cortex that is more deeply placed in the lateral sulcus in comparison to that of M. fascicularis. A small annectant gyrus provides a guide to the position of the primary auditory area.

Recently, a cognitive function of cerebellar networks has been challenging the traditional view of the cerebellum as a motor control centre. Among the cognitive abilities reported to be affected by cerebellar deficits is the capacity to solve a spatial problem. We investigated the influence of a cerebellar lesion on spatial abilities by behavioural analysis of rats that had undergone surgical hemicerebellectomy (HCb; HCbed rats). Experiments were performed with a Morris water maze (MWM) and a water T-maze in both cue and place versions (visible or hidden platform respectively). Results indicate a severe impairment in coping with spatial information in all phases of MWM testing as well as in the T-maze paradigm. However, if the MWM cue phase was prolonged, HCbed rats displayed some ability to learn platform position, although at a level significantly different from controls. They succeeded in finding the platform, even in a pure place paradigm, such as finding a hidden platform with the starting points sequentially changed. Retention testing was also performed, demonstrating that HCb affects acquisition but not retention of spatial information. HCbed animals exhibit such disrupted exploration behaviour that they can display only peripheral circling, and they can acquire spatial relations only when proximal cues are available. Furthermore, in all phases of testing, platform finding for HCbed animals is essentially based on place strategies. Thus, a specific pattern of spatial behaviour, markedly different from that displayed following hippocampal or cortical lesions, characterizes cerebellar lesioned rats. These results are discussed taking into account the role in procedural learning recently assigned to cerebellar networks, demonstrating that the cerebellar circuits represent the keystone of the procedural components of spatial event processing.