Cortical areas in the medial frontal lobe of the cat delineated by quantitative analysis of thalamic afferents.
The aim of these experiments was to establish the number and location of connectionally distinct areas in the medial frontal lobe of the cat. Thirty deposits of distinguishable retrograde tracers were placed at restricted sites spanning the medial frontal lobe in 16 cats. Following each deposit, the number of retrogradely labeled neurons in each of 17 thalamic nuclei was determined. Variations of the thalamic labeling pattern dependent on the location of the cortical tracer deposit were then analyzed by a quantitative procedure. The results indicate that the medial frontal lobe contains three fundamental divisions: the anterior cingulate area, medial area 6, and the medial prefrontal district. The anterior cingulate area derives its strongest thalamic input from the anteriomedial nucleus. Medial area 6 is the target of afferents originating in a dorsolateral sector of the mediodorsal nucleus and in the ventroanterior nucleus. Medial prefrontal cortex is heavily innervated by pathways originating in the core of the mediodorsal nucleus and in the principal ventromedial nucleus. Within each major district, thalamic connectional patterns exhibit graded regional variation, with the result that, whereas the connections of the district are not uniform, it is difficult to define further discrete subdivisions. We discuss these results in relation to previously proposed schemes for paracellation of the cat's medial frontal lobe and conclude that the infralimbic and prelimbic areas (areas 25 and 32) of previous systems are best understood not as discrete areas but as ventral and intermediate sectors of a continuous medial prefrontal domain.
Musil
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Laboratory for Sensorimotor Research, National Institutes of Health, Bethesda, Maryland 20892.
Olson
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D000344:Afferent Pathways / Q000166:cytology; D000818:Animals; D002415:Cats; D005625:Frontal Lobe / Q000166:cytology*; D013787:Thalamic Nuclei / Q000166:cytology*