Reciprocal connections between the claustrum and the gyrus sigmoideus posterior in the cat. An experimental study using the antegrade degeneration methods and the HRP retrograde axonal transport.

Following coagulation lesions affecting the gyrus sigmoideus posterior we investigated the termination field of the cortico-claustral projection using impregnation techniques (NAUTA, GYGAX 1954; FINK, HEIMER 1967). Preterminal and terminal fragments of the degenerating axons were identified ipsilaterally on the dorsal and lateral margins of the claustrum dorsale in the rostral half of the nucleus. Labeled neurons were found ipsilaterally within the claustrum dorsale, in the termination field of the cortico-claustral projection rising from the gyrus sigmoideus posterior following injections of HRP (Sigma VI) into the gyrus sigmoideus posterior. There are reciprocal connections between the dorsolateral region of the claustrum dorsale and the cortex of the gyrus sigmoideus posterior. A prevailing number of the HRP-positive neurons of the claustrum are located in the termination field of the particular cortico-claustral projection. The discussion deals with some problems concerning the cortico-claustral and claustro-cortical projections and presents opinions as to the functional significance of the claustrum.