Interactions between the pulvinar and cortex are functionally and numerically important. Yet, the organization of this system at the level of microcircuitry is poorly understood by comparison with other major cortically-linked centers, such as the basal ganglia and the specific sensory thalamic nuclei. In this project, we will use high resolution serial axon reconstruction and neuron analysis to test and refine the general hypothesis that principles derived from specific sensory pathways do not apply to associational thalamic nuclei and to their cortical connectivity. Preliminary results illustrate the promise of this approach. For example, we now have evidence for two types of corticopulvinar terminations: 1) small, spherical arbors with large beaded endings, and 2) elongated terminations, diverging over several millimeters, with spinous terminal specializations (see Appendix:Rockland, 1994a). These may originate from two previously identified populations of corticopulvinar neurons; namely, giant and medium pyramids of layer 5. We hypothesize that events sampled by pyramids with wide dendritic fields are """"""""compressed"""""""" to a delimited terminal focus in the pulvinar, whereas more localized analysis (performed by the more numerous medium pyramids) is distributed over an assembly of pulvinar neurons. Different synaptic mechanisms are also likely to be associated with the large beaded vs. spinous specializations. Four experiments are proposed. Two will use PHA-L to identify corticopulvinar and pulvinocortical axons. These will be analyzed as projection foci, and reconstructed in serial sections to determine such parameters as axon caliber, branching, arbor size and shape, and density of terminations. A third experiment will use combined in vivo/in vitro filling to carry out a detailed mapping of the two populations of corticopulvinar projection neurons, in terms of morphometric and geometric features of their dendritic phenotype. We will apply quantitative methods to determine the density of giant corticopulvinar neurons, their proportion to medium corticopulvinar neurons, and area-specific differences. A fourth experiment addresses the topographic organization and convergence of corticopulvinar connections. Two anterograde tracers will be injected into visuotopically corresponding foci of two cortical areas. These data may illuminate questions arising from psychophysical, physiological and clinical observations, as these relate to the role of the pulvinar in selective visual attention. The identification of two pyramidal phenotypes, distinguished by soma size, dendritic arbor, and extrinsic axon terminations, may be relevant 1) to separate subcomponents of attention mechanisms; and 2) as a connectionally-specific model supporting further molecular and functional characterization. In other systems such as the geniculocortical, axon microcircuitry has provided a useful baseline for design in interpretation of studies related to plasticity effects, and the proposed program of research may promote similar applications.

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Research Project (R01)
Project #
5R01MH053598-03
Application #
2460385
Study Section
Cognitive Functional Neuroscience Review Committee (CFN)
Project Start
1995-08-01
Project End
2000-07-31
Budget Start
1997-08-01
Budget End
1998-07-31
Support Year
3
Fiscal Year
1997
Total Cost
Indirect Cost
Name
University of Iowa
Department
Neurology
Type
Schools of Medicine
DUNS #
041294109
City
Iowa City
State
IA
Country
United States
Zip Code
52242
Ding, S L; Rockland, K S (2001) Modular organization of the monkey presubiculum. Exp Brain Res 139:255-65
Rockland, K S; Knutson, T (2001) Axon collaterals of Meynert cells diverge over large portions of area V1 in the macaque monkey. J Comp Neurol 441:134-47
Ding, S L; Van Hoesen, G; Rockland, K S (2000) Inferior parietal lobule projections to the presubiculum and neighboring ventromedial temporal cortical areas. J Comp Neurol 425:510-30
Rockland, K S; Knutson, T (2000) Feedback connections from area MT of the squirrel monkey to areas V1 and V2. J Comp Neurol 425:345-68
Rockland, K S; Andresen, J; Cowie, R J et al. (1999) Single axon analysis of pulvinocortical connections to several visual areas in the macaque. J Comp Neurol 406:221-50
Rockland, K S (1998) Convergence and branching patterns of round, type 2 corticopulvinar axons. J Comp Neurol 390:515-36
Rockland, K S (1998) Complex microstructures of sensory cortical connections. Curr Opin Neurobiol 8:545-51
Anderson, J C; Binzegger, T; Martin, K A et al. (1998) The connection from cortical area V1 to V5: a light and electron microscopic study. J Neurosci 18:10525-40
Rockland, K S (1996) Two types of corticopulvinar terminations: round (type 2) and elongate (type 1). J Comp Neurol 368:57-87