During the past years brain imaging techniques like positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) became more and more important for gaining new insights into processes of and circuits for memory encoding and retrieval. These findings also had a great impact on a better understanding of memory dysfunctions and their underlying brain mechanisms. In the present review, data on memory dysfunctions are analyzed separately according to whether they are of an organic, or a psychiatric psychogenic etiology. Studies examining patients with various forms of amnesia and dementia, for whom functional brain imaging data were available, indicate early functional brain changes. These early changes differ from subsequent structural brain changes and therefore support the clinical and diagnostic use of functional brain imaging techniques in memory disturbances. Furthermore, research outcomes from patients suffering from psychogenic amnesias (dissociative amnesias) and psychogenic fugue conditions are summarized. Finally, differences and similarities between organic amnesia and psychogenic amnesia are discussed with regard to the present literature and exemplified with two single cases from our lab.

Human behavior strongly relies on the visual storage of events. Unfortunately, the sense of sight is susceptible to numerous distortions and misidentifications. Our study investigated the possibility of applying neuroimaging methods for verification of eyewitness reports. We developed a film paradigm and investigated three related picture sets in a recognition task using functional magnetic resonance imaging (fMRI). For each picture subjects were instructed to make a known-unknown decision. Behavioral results showed false recognitions for nearly half of the presented stimuli. The fMRI results revealed distinct activations for correct and false recognitions. The orbitofrontal cortex could be distinguished as a key region for processing imagined and distorted information resulting in correct rejection of unknown material. Otherwise, false recognitions of unknown material highlighted surprising activation within the posterior cingulate gyrus indicating the subjects' strain to match unknown information to that known. The results are discussed in terms of current false memory research.

We designed a laboratory study to investigate the influence of social interaction on category learning. The objective in the present study is to examine what kind of teaching behavior can improve an agent's learning of categories. In a computerbased study participants learned four categories for sixteen objects which appear on a computer screen. The objects' categories determine what kind of manipulation is to be done on the objects. Five tutors and twenty participants were recruited to participate. For the study the tutors were placed in front of a computer in one room whereas the learners were in another room. The learners' task was to manipulate the objects appropriately through the instructions they received from the tutor on their screens via six symbols. These six symbols were the only way for the tutor to communicate with the learner. We call this a bottom-up learning as the it relies entirely on the perception of the tutors' symbols without any prior knowledge of their meaning. The focus in the present study is not on the ability by the learner to acquire knowledge of the categories but on the types of instructions that the tutor gave during the trials and the effects of the feedback given to the learner. Therefore, the feedback given by the tutors via the symbols was classified and quantified.