Donders Institute for Brain, Cognition and Behaviour
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Thesis defense Selma Lugtmeijer (Donders series 450)

25 September 2020

Promotors: prof. dr. E. de Haan (Universiteit van Amsterdam),
prof. dr. R. Kessels (Radboud Universiteit), prof. dr. F. de Leeuw (Radboudumc)
Co-promotor: dr. L. Geerligs (Radboud Universiteit)

Neurocognitive mechanisms of visual working memory and episodic memory in healthy aging and after stroke

Our surroundings consist of scenes and objects that have a multitude of visual features: shape, color, texture, size, orientation, and location. We are able to remember which object was where and what features belong to it by forming an internal representation of features and their conjunctions. Some representations only last for a brief period, they are kept in working memory, while other representations remain over a longer period of time, known as episodic memory.

The aim of this thesis was to investigate how memory subsystems relate at a behavioral and neural level using novel behavioral paradigms, lesion-symptom mapping, and computational modeling, in healthy adults and stroke patients.

Lesions studies in this thesis support the notion of a widely distributed frontoparietal network underlying memory, with a suggestion of specialization for memory subsystems (working memory and episodic memory; feature reporting and binding) and multiple visual representations in the brain. Representations in different areas might compensate for impaired encoding in lesioned areas explaining mostly subtle visual memory impairments following stroke.

Experimental studies in this thesis showed that, at a group level, controls outperform patients and younger adults perform better than older adults. At the same time, selective deficits in different subsystems of visual memory are prevalent. This indicates that different neural mechanisms may be involved. It also stresses the need for broad memory examination, as selective memory deficits might easily be missed in standard clinical assessment where testing mainly with verbal materials and with a maximum delay of 30 minutes is the standard.