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Fluidity of functional ensembles in the infralimbic cortex of rats during reward seeking

Sonntag, Ivo

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The medial prefrontal cortex (mPFC), specifically the prelimbic (PL) and the infralimbic region (IL), plays a crucial role during reward seeking behaviour. The IL specifically is involved in the control of reward seeking and has been implicated in the representation of different rewards. However, the precise representation of reward seeking behaviour on a neuronal network level within the IL remains elusive. To investigate neuronal ensembles during reward seeking in the IL of the mPFC in rats, an operant conditioning paradigm was combined with imaging of the intracellular calcium concentration ([Ca2+]i) as a proxy for neuronal activity. The latter is achieved using GRIN lenses and miniaturized head-mounted fluorescence microscopes. A frame trigger was used to synchronize the operant conditioning chambers with the [Ca2+]i data and an analysis pipeline was developed using a combination of custom designed Matlab classes and available open source software. Neurons were identified for three saccharin self-administration (SA) and one reinstatement (RE) session and then matched across sessions. Periods during which rats interacted with the operant conditioning setup were identified (e.g. lever presses and head entries into the reward port) and the corresponding [Ca2+]i transients were used to identify neurons coactive during distinct phases of reward seeking behaviour. Neurons were classified according to the time point of their activity relative to the sequence of actions consisting of the lever press and the time before, during, and after the head entry. This analysis revealed that subsets of neurons are preferentially active during distinct events of the reward seeking. Also, cells tuned to time points during the reward seeking did not appear or show tuning in all of the sessions. If they did show tuning, however, the phase of the reward seeking to which they showed tuning generally remained the same. Hence, the specific ensemble which is active during the reward seeking in each session changes. Individual neurons that are recruited into these ensembles, however, keep their tuning. Also, the composition of tuned neurons active during a specific behavioural phase remains stable. In addition, neurons that are active and tuned in multiple sessions do not appear to be arranged in a topology that can be identified with the methods used. In conclusion, the sequence of the reward seeking behaviour is encoded in neuronal ensembles of the IL cortex. These ensembles are formed from a larger pool of available neurons in each session. Neurons participating in these ensembles preferentially keep their tuning to a phase of the reward seeking, but may not be recruited to each of the ensembles. Thus, ensembles representing identical behavioural episodes in different sessions are not stable, but fluidly change their composition.

Item Type: Dissertation
Supervisor: Kuner, Prof. Dr. Thomas
Place of Publication: Heidelberg
Date of thesis defense: 28 February 2020
Date Deposited: 15 Sep 2020 10:07
Date: 2020
Faculties / Institutes: The Faculty of Bio Sciences > Dean's Office of the Faculty of Bio Sciences
Medizinische Fakultät Heidelberg > Institut für Anatomie und Zellbiologie
Subjects: 570 Life sciences
600 Technology (Applied sciences)
Controlled Keywords: Mikroskopie, Verhaltensforschung
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