Parallel pathways inmacaque monkeystriate cortex: Anatomically defined columns inlayer III

Visual information reaching striate cortex comesfromparallel pathways, andtheinformation isorga- nized, orprocessed, bythelayers andcolumns ofstriate cortex. Tobetter understand howthis isaccomplished anatomically, weasked whether parallel pathways originating inthelateral geniculate nucleus (LGN), andterminating separately inlayer IV,remain separate inlayer Imofmacaque monkeys. Layer m isofinterest since itmayplayaspecial role incolor andform vision butnotinanalysis ofvisual motion. Thechief finding was thatcells in"blobs" oflayer m thatstain densely forcy- tochrome oxidase receive indirect input, vialayer IVC,from bothLGNmagnocellular (M)andparvocellular (P)cells. This isimportant because thePandM pathways mayrepresent color/form andmotion-processing channels, respectively. In- terblob cells receive indirect input, vialayers IVCandIVA, fromtheLGNPcells. Also, assuggested byothers, ourdata demonstrate that layer HIcanbesubdivided. Thebottom tier, layer ITB,receives direct projections fromallcortical layers. Output fromlayer HMBappears toremain intrinsic tostriate cortex. Incontrast, thetoptier, layer IlA,receives projections fromlayer ITBaswell asfromlayers IVA,IVB(blobs only), andV,butitreceives nodirect projections fromLGNrecipient layers IVCandVI.Unlike layer hUB,theoutput oflayer HIA reaches extrastriate areas. Thus, impulses arriving frompar- allel LGNpathways mayberecombined through serial stages instriate cortex toproduce asetofparallel pathways that are qualitatively different fromtheoriginal LGNset. Theearly stages oftheprimate visual system arecharacter-