Brain Differently Changes its Algorithms in Parallel Processing of Visual Information

Abstract

Abstract. Feedback from the visual cortex (Vl) to the Lateral G(-miculate Nucleus (LGN) in macaque monkey increase contrast gain of LGN neurons for black and white (B&VV) and for color (C) stimuli. LGN parvocellular cells responses to B&\i\1 gratings are enhanced by feedback multiplicatively and in contrast independent manner. However, in magnocellular neurons corticofngal pathways enhance cells responses in a contrast~dependent non-linear manner. For C stimuli cortical feedback enhances parvocellular neurons responses in a very strong contrast-dependent manner. Ba...<;ed on these results [13] we propose a model which includes excitatory and inhibitory effects on cells activity (shunting equations) in retina and LGN while taking into account the anatomy of cortical feedback connections. The main mechanisms related to different algorithms of the data processing in the visual brain are differences in feedback properties from Vl to parvocellular (PC) and to magnocdlula.r (MC) neurons. Descending pathways from Vl change differently receptive field (RF) structur(~ of PC and MC cells. For B&W stimuli, in PC cells feedback changes gain similarly in the RF center and in the RF surround, leaving PC RF structure invariant. However, feedback influence ?viC cells in two ways: directly and throughLGN intcrneurons, which together changes gain and si,es of their RF center differently than gain and size of the RF surround. For C stimuli PC cells operate like M C cells for B& \'f...T. The first mechanism extracts from t.he stimulus an important features in a independent way from other stimulus parameters 1 whereas the second channel changes its tuning properties as a function of other stimulus attributes like contrast and/or spatial extension. The model suggests novel idea about the possible functional role of PC and MC pathways.