The neural mechanisms underlying conscious recognition remain unclear, particularly the roles played by the prefrontal cortex, deactivated brain areas and subcortical regions. We investigated neural activity during conscious object recognition using 7 Tesla fMRI while human participants viewed object images presented at liminal contrasts. Here, we show both recognized and unrecognized images recruit widely distributed cortical and subcortical regions; however, recognized images elicit enhanced activation of visual, frontoparietal, and subcortical networks and stronger deactivation of the default-mode network. For recognized images, object category information can be decoded from all of the involved cortical networks but not from subcortical regions. Phase-scrambled images trigger strong involvement of inferior frontal junction, anterior cingulate cortex and default-mode network, implicating these regions in inferential processing under increased uncertainty. Our results indicate that content-specific activity in both activated and deactivated cortical networks and non-content-specific subcortical activity support conscious recognition.

Learning to associate the context in which a stimulus occurs is an important aspect of animal learning. We propose that the association of an olfactory stimulus with its multisensory context is mediated by projections from ventral hippocampus (vHC) networks to the anterior olfactory nucleus (AON). Using a contextually cued olfactory discrimination task, rats were trained to associate 2 olfactory stimuli with different responses depending on visuospatial context. Temporary lesions of the AON or vHC impaired performance on this task. In contrast, such lesions did not impair performance on a noncontextual olfactory discrimination task. Moreover, vHC lesions also impaired performance on an analogous contextually cued texture discrimination task, whereas AON lesions affected only olfactory contextual associations. We describe a distinct role for the AON in olfactory processing and conclude that early olfactory networks such as the olfactory bulb and AON function as multimodal integration networks rather than processing olfactory signals exclusively.

Visual Abstract

AbstractLearning to associate the context in which a stimulus occurs is an important aspect of animal learning. We propose that the association of an olfactory stimulus with its multisensory context is mediated by projections from ventral hippocampal networks (vHC) to the anterior olfactory nucleus (AON). Using a contextually-cued olfactory discrimination task, rats were trained to associate two olfactory stimuli with different responses depending on visuo-spatial context. Temporary lesions of the AON or vHC impaired performance on this task. In contrast, such lesions did not impair performance on a non-contextual olfactory discrimination task. Moreover, vHC lesions also impaired performance on an analogous contextually-cued texture discrimination task, whereas AON lesions affected only olfactory contextual associations. We describe a distinct role for the AON in olfactory processing, and conclude that early olfactory networks such as the olfactory bulb and AON function as multimodal integration networks rather than processing olfactory signals exclusively.Significance statementContextual information has long been known to play a key role in cognitive functions such as memory and decision making. We here show the contextual modulation of neural information in early primary sensory networks and its effects on contextually conditional learned behavior. We propose that projections from ventral hippocampus to anterior olfactory nucleus convey contextual information to the early olfactory system, modulating sensory representations and olfactory perception. Using behavioral pharmacology and computational modeling, we show how established network structures can mediate multimodal information and use context to make olfactory decisions.

No abstract