5a,b). stable spatial maps and strong remapping of place fields toward the goal location. mice showed a significant learning deficit accompanied by reduced spatial map stability and the absence of goal-directed place cell reorganization. These results expand our understanding of the hippocampal ensemble dynamics supporting cognitive flexibility and demonstrate their importance in a model of 22q11.2-associated cognitive dysfunction. Episodic memory, the encoding of personal experience organized in space and time, is usually a fundamental aspect of cognition1. Episodic memory dysfunctions are highly debilitating symptoms QNZ (EVP4593) of various neurological, cognitive and psychiatric disorders, including schizophrenia (SCZ)2. Cognitive deficits in general appear to be the strongest predictor of SCZ patients functional outcomes3; however, neural circuit dynamics supporting episodic memory and the manner in which they fail in SCZ remains poorly understood. To this end, we analyzed a well characterized animal model of cognitive dysfunction and SCZ, the mouse model of the 22q11.2 deletion syndrome (22q11.2DS)4. The well documented role of the hippocampus in episodic and spatial memory1,5C7, combined with morphological and functional alterations of the hippocampus in SCZ patients8,9, collectively points to a central role of this brain area in the pathophysiology of cognitive memory deficits in SCZ10. In particular, physiological and morphological alterations have been reported specifically in area CA1the hippocampal output nodein SCZ patients11, suggesting a potentially primary role for this area in disease pathophysiology. Principal cells throughout the hippocampus are selectively active in specific locations within an environment (place cells)12. Place cells collectively form cognitive maps representing spatial components of episodic memories6,13, the long-term stability of which is a widely posited prerequisite for reliable learning14C18. QNZ (EVP4593) Place cell map stability is affected by attentional and task demands, and place cell maps also incorporate goal-related information during learning15,19C25. In particular, reorganizing ATN1 place cell maps to enrich goal locations was found to predict memory performance26. Therefore, monitoring place cell ensemble dynamics during goal-directed learning may provide a tractable entry point for understanding how episodic memory deficits arise from genetic mutations associated with QNZ (EVP4593) SCZ. Two-photon Ca2+ imaging in awake mice during head-fixed behaviors allows for the chronic recording of physiological activity from individual place cells, as well as their ensemble activity as a whole. By tracking the activity of place cell populations in mice and wild-type (WT) littermates through each phase of a goal-oriented learning task, we identified specific aspects of place cell map stability QNZ (EVP4593) that evolved with learning, as well as alterations in the stability and plasticity of these cognitive maps in the mutant mice. Our findings highlight reduced stability and impaired goal-directed reorganization of hippocampal place cells as fundamental components of 22q11.2-deletion-linked cognitive dysfunction. RESULTS mice are impaired in a head-fixed goal-oriented learning task upon changes in both context and reward location To facilitate chronic recording from hippocampal CA1 place cells during learning, we designed a head-fixed variation of goal-oriented learning (GOL; Fig. 1a,b and Online Methods) tasks that have been previously used in freely moving rodents26, allowing for chronic two-photon functional Ca2+ imaging. Our task consisted of three sessions per day, with 3 days (d) for each of three conditions (27 total sessions per mouse). In Condition I, mice learned a single fixed reward location, then remembered that location while the environmental context and local cues were altered (Online Methods) in Condition II, and the reward was moved in Condition III. Open in a separate window Figure 1 Differences in learning performance between and WT mice in GOL task. (a) The three conditions of the GOL task. Mice spend 3 d in each condition. Contexts A and A are composed of different auditory, visual, olfactory and tactile cues (Online Methods), varied between Condition I and Condition II. The location of the hidden reward (blue circles, Rew 1 and Rew 2) is switched between Condition II and Condition III. Water-deprived mice trained to run on a linear treadmill were introduced to a novel environmental context (Context A) consisting of a feature-rich fabric belt and specific background with nonspatial odor, tones and blinking light patterns (Context A) on the first day of the experiment. Operant water rewards were available at a single unmarked.