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Markus Kiefer

Publications and source records attributed to Markus Kiefer.

5 recordsLinked to original sources
PubMed2003

Executive control deficit in depression: event-related potentials in a Go/Nogo task.

Growing evidence suggests an impairment of executive control functions in depression. The aim of this study was to investigate whether depressive patients show a specific impairment of executive control in a response inhibition task and to investigate its neurophysiological correlates using event-related potentials. We analyzed data from 16 patients with unipolar depression and 16 healthy controls using an auditory Go/Nogo task. High resolution event-related potentials (ERPs) were recorded. Depressive patients performed similar to controls in the Go task, but worse in the Nogo task, which required response inhibition. ERPs revealed the neurophysiological correlate of this deficit. Both groups showed the same voltage pattern in the Go task. However, in the Nogo task depressive patients showed a reduction of an early fronto-temporal positivity in the N2 time window, which was associated with response inhibition in healthy subjects. This effect could not be explained by increased task difficulty in the Nogo task. There was no difference between groups in later stages of processing as indexed by the P3 complex. Therefore, the findings suggest a specific deficit in response inhibition, which requires executive control. This deficit is thought to reflect dysfunctional activation of the network subserving executive control during an early stage of cortical processing.

Adult↗
PubMed2003

Emotional context modulates subsequent memory effect.

Emotions have been shown to modulate memory processes. However, the neuronal substrate underlying these modulatory effects is largely unknown. Using event-related functional magnetic resonance imaging (fMRI), we investigated whether the context of emotional encoding modulates brain activation predictive for subsequent recall of emotionally neutral material. While inferior frontal activation predicted recall in general, our data show that in a positive encoding context, recall was predicted by activation of right anterior parahippocampal and extrastriate visual brain areas, whereas in a negative encoding context, recall was predicted by activation of the amygdala. Thus, we could demonstrate that successful episodic encoding is differentially modulated by emotional context. These results contribute to the understanding of the interaction of emotion and cognition and moreover are of general relevance for studies of episodic memory.

Adult↗
PubMed2002

Human anterior cingulate cortex is activated by negative feedback: evidence from event-related potentials in a guessing task.

It has been controversially discussed whether the error-related negativity (ERN) or error negativity (N(e)), an electrophysiological index of anterior cingulate activation, reflects response conflict or response evaluation subserving error monitoring processes. We investigated event-related potentials (ERPs) in a guessing task which did not induce response conflict. Subjects had to guess which of the four aces of a French card play would be presented next and received feedback at random. We observed a negative ERP deflection in trials following negative feedback which was identified as ERN/N(e). Dipole analysis of scalp potentials indicated sources in the anterior cingulate and left inferior prefrontal cortex. The observation of the ERN/N(e) following negative feedback during guessing suggests that this ERP component mirrors response evaluation processes comparing expected and actual response outcome rather than response conflict.

Adult↗
PubMed2002

The N400 is modulated by unconsciously perceived masked words: further evidence for an automatic spreading activation account of N400 priming effects.

It is a matter of debate whether the N400 component of the event-related brain potential (ERP) is sensitive to unconscious automatic priming mechanisms or to strategic mechanisms only. Recent studies demonstrated N400 modulation by masked primes at a short SOA supporting an automatic spreading activation account. However, it cannot be ruled out that strategic mechanisms based upon partial prime identification contributed to the observed priming effects. The present study was set up to substantiate masked N400 priming effects as an index of automatic spreading activation. It was assessed whether partial identification of the masked words due to backward priming could have supported strategic priming to occur. In experiment 1, ERPs were recorded while subjects performed lexical decisions on targets preceded by masked and unmasked primes at an SOA of 67 ms. Masked words, which were not consciously perceived, as well as visible words were shown to modulate the N400 to meaningfully related target words. Experiment 2 required subjects to perform decisions on visual, lexical and semantic features of masked words presented with or without semantically related context words. Subjects performed at chance in all tasks. Furthermore, the results exclude the possibility that backward priming has rendered the masked words partially visible. The present study therefore demonstrates that N400 priming effects can be reliably obtained from unconsciously perceived masked words at a very short SOA and strengthens the notion that the N400 is modulated by automatic spreading activation and not exclusively by strategic semantic processes.

Adult↗