Morphology and connections of neurons in area 17 projecting to the extrastriate areas mt and 19DM and to the superior colliculus in the monkey Callithrix jacchus

Abstract

Neurons of area 17, the primary visual cortex, project to various anatomically and physiologically different extrastriate areas and subcortical regions. In the present investigation, we addressed the question of whether the efferent neurons in area 17 can contribute to functional diversity between these regions. We approached this question by analyzing the dendritic morphology of neurons in area 17 projecting to area MT, area 19DM, and the superior colliculus in the new world simian primate Callithrix jacchus, because dendritic morphology is an important factor in determining physiological properties of nerve cells. Retrograde transport of fluorochromes injected into the target regions, and intracellular injections of Lucifer yellow in the prelabelled neurons, revealed the following. 1) Morphologically identical large pyramidal cells in layer VI of area 17 project to all three targets. Some of them possess axon collaterals to two or all three targets, suggesting that they provide common information to all three areas. 2) Pyramidal cells in layer IIIc projecting to area MT form a morphologically homogeneous population. 3) Three small to medium-sized pyramidal cell types in layers IIIa-c, spiny stellate cells in layer IIIc, and another large pyramidal cell type in layer VI project to area 19DM. 4) Pyramidal cells in the lower two-thirds of layer V in area 17 project to the superior colliculus. In conclusion, we have shown that in Callithrix one efferent pathway may originate from several cell types. However, with the exception of the large cells in layer VI, efferent cells projecting to area MT, area 19DM, and the superior colliculus were morphologically distinct. This suggests that functional differences between brain regions could arise in part from morphological heterogeneity between and within the efferent cell populations.

Connections of the Dorsomedial Visual Area: Pathways for Early Integration of Dorsal and Ventral Streams in Extrastriate Cortex

“…The V1 projection was almost exclusively formed by supragranular neurons (%SLN ϭ 99.7). In agreement with previous studies (vogt Weisenhorn et al, 1995;, the majority of neurons projecting to DM were located deep in layer 3 [i.e., in what is traditionally referred to as Brodmann's "layer IVb" (Casagrande and Kaas, 1994) (supplemental Fig. 1, available at www.jneurosci.org as supplemental material)].…”

“…In area V1, we have considered the granular layer to correspond to Brodmann's layer IVc, given that this is the most likely homolog of layer 4 in other areas (for details, see Casagrande and Kaas, 1994). According to the nomenclature proposed by these authors, the sublayer of V1 that forms the main projection to areas DM and MT (Brodmann's layer IVb) is considered to represent deep layer 3 (layer 3c) [see also vogt Weisenhorn et al (1995) and supplemental Fig. 1 (available at www.jneurosci.…”

The second visual area in the marmoset monkey: Visuotopic organisation, magnification factors, architectonical boundaries, and modularity

“…surprises. Briefly, whereas the myeloarchitectural appearance of V1 is dominated by the stria of Gennari, which is absent from V2, the DM cortex is far more myelinated than V2 (e.g., Kaas, 1971, 1975;Gattass et al, 1987;Krubitzer and Kaas, 1993;Rosa and Schmid, 1995;Vogt Weisenhorn et al, 1995). In flat-mounted preparations, the borders between V1, V2, and DM are also evident.…”

Phosphene Induction and the Generation of Saccadic Eye Movements by Striate Cortex

“…Much evidence supports this contention. First, the deepest layers of V1 innervate the superior colliculus (Finlay et al 1976;Fries 1984;Graham 1982;Spatz et al 1970;Vogt-Weisenhorn et al 1995). Second, the lowest current threshold and shortest latencies for evoking saccades electrically occur with stimulation of the deepest layers of V1 .…”

“…This line of work, however, was largely eclipsed by the seminal single-unit recording experiments of Hubel and Wiesel. Nevertheless, a number of investigators have continued to use electrical stimulation techniques to ascertain V1 function as it pertains to ocular and visual responses in primates (Bartlett and Doty 1980;DeYoe 1983;Doty 1970;Keating and Gooley 1988;Keating et al 1983;Schiller 1972Schiller , 1977. Anatomical studies have shown that the deepest layers of V1 (i.e., lamina V) innervate the superior colliculus (Fries 1984;Graham 1982;Spatz et al 1970;Vogt-Weisenhorn et al 1995). The superior colliculus mediates oculomotor responses (Schiller 1984;Wurtz et al 2001).…”