Mouse prefrontal cortex represents learned rules for categorization

Abstract

The ability to categorize sensory stimuli is crucial for an animal’s survival in a complex environment. Memorizing categories instead of individual exemplars enables greater behavioural flexibility and is computationally advantageous. Neurons that show category selectivity have been found in several areas of the mammalian neocortex1–4, but the prefrontal cortex seems to have a prominent role4,5 in this context. Specifically, in primates that are extensively trained on a categorization task, neurons in the prefrontal cortex rapidly and flexibly represent learned categories6,7. However, how these representations first emerge in naive animals remains unexplored, leaving it unclear whether flexible representations are gradually built up as part of semantic memory or assigned more or less instantly during task execution8,9. Here we investigate the formation of a neuronal category representation throughout the entire learning process by repeatedly imaging individual cells in the mouse medial prefrontal cortex. We show that mice readily learn rule-based categorization and generalize to novel stimuli. Over the course of learning, neurons in the prefrontal cortex display distinct dynamics in acquiring category selectivity and are differentially engaged during a later switch in rules. A subset of neurons selectively and uniquely respond to categories and reflect generalization behaviour. Thus, a category representation in the mouse prefrontal cortex is gradually acquired during learning rather than recruited ad hoc. This gradual process suggests that neurons in the medial prefrontal cortex are part of a specific semantic memory for visual categories.

Visual association cortex links cues with conjunctions of reward and locomotor contexts

“…36 selectively by one cue in contexts where the cue has become familiar and nonsalient may constitute a kind of extinction trace, as observed in other brain areas. 12,37 Our finding that learned cue responses in POR depend on conjunctions of reward/locomotion contexts builds on prior studies of this region focusing largely on spatial context. 7,8,38,39 Is locomotion truly an internal context in a similar sense as spatial context?…”

“…3,10 Identifying the appropriate meaning of visual cues in specific reward and spatial contexts likely involves inputs to POR from neurons encoding both cues and reward in basolateral amygdala 3 and from neurons encoding spatial and nonspatial contexts in entorhinal and prefrontal cortex. [11][12][13] Studies in naive animals show that cue responses in primary visual cortex (V1) and nearby areas are strongly influenced by ''internal'' contexts [14][15][16][17][18] (e.g., locomotion). Furthermore, the transition between stationary and locomotor contexts reconfigures the dialogue between individual V1 neurons and distinct cortical regions.…”

Prelimbic cortex maintains attention to category-relevant information and flexibly updates category representations

“…We predict that this is mediated by the PL; therefore, inactivating the PL will impair learning for the 1D tasks. This prediction is supported by calcium imaging in the mouse medial frontal cortex during a go/no-go version of the 1D task ( Reinert et al, 2021 ). This prediction also aligns with Love & Gureckis (2007) , who proposed that the PFC is synonymous to the selective attention mechanism of the neural network model SUSTAIN (Supervised and Unsupervised STratified Adaptive Incremental Network; Love, Medin, & Gureckis, 2004 ).…”

Use of Active Salmon-Lecithin Nanoliposomes to Increase Polyunsaturated Fatty Acid Bioavailability in Cortical Neurons and Mice

“…In our study, the significant cortical FA levels in adult mice with normal n-3 levels illustrate the possibility of enriching this brain region with PUFAs. This cerebral structure plays an important role in processing sensory information [59], social cognition [60], high cognitive processes such as working memory, attentional control, reasoning, decision making [61], and category learning and categorization [62]. Analysis of the total amount of lipids in each tissue over time revealed a significant increase in the quantity of cortical lipids at the end of NL treatment, as compared to controls, which may have been due to the higher levels of FAs found in this tissue compared to the control group.…”