Biomedical subjects

Gregor Joppich

Publications and source records attributed to Gregor Joppich.

3 recordsLinked to original sources

PubMed2004

Brain potentials and self-paced random number generation in humans.

Random number generation (RNG) requires executive control. A novel paradigm using the eight drum pads of an electronic drum set as an input device was used to test 15 healthy subjects who engaged in random or ordered number generation (ONG). Brain potentials time-locked to the drum-beats revealed a more negative response during RNG compared to ONG which had a left frontal distribution. Source analysis pointed to Brodmann area 9, which has been reported previously in a PET study and is thought to be engaged in suppression of habitual responses such as counting up in steps of one during RNG. Lateralized readiness potentials reflecting the difference in activation of the contra and ipsilateral motor cortex were smaller during ONG reflecting the ability to preprogram such canonical sequences.

Adult↗

PubMed2004

Brain potentials index executive functions during random number generation.

The generation of random sequences is considered to tax different executive functions. To explore the involvement of these functions further, brain potentials were recorded in 16 healthy young adults while either engaging in random number generation (RNG) by pressing the number keys on a computer keyboard in a random sequence or in ordered number generation (ONG) necessitating key presses in the canonical order. Key presses were paced by an external auditory stimulus to yield either fast (1 press/800 ms) or slow (1 press/1300 ms) sequences in separate runs. Attentional demands of random and ordered tasks were assessed by the introduction of a secondary task (key-press to a target tone). The P3 amplitude to the target tone of this secondary task was reduced during RNG, reflecting the greater consumption of attentional resources during RNG. Moreover, RNG led to a left frontal negativity peaking 140 ms after the onset of the pacing stimulus, whenever the subjects produced a true random response. This negativity could be attributed to the left dorsolateral prefrontal cortex and was absent when numbers were repeated. This negativity was interpreted as an index for the inhibition of habitual responses. Finally, in response locked ERPs a negative component was apparent peaking about 50 ms after the key-press that was more prominent during RNG. Source localization suggested a medial frontal source. This effect was tentatively interpreted as a reflection of the greater monitoring demands during random sequence generation.

Adult↗

PubMed2003

Tracking of multiple sound sources defined by interaural time differences: brain potential evidence in humans.

Among other cues, interaural time differences (ITD) can be used to compute the location of a sound. To investigate whether ITD can be used for the preattentive detection of sounds coming from a different location than standard sounds (P=0.7, no ITD), left and right 'far' (900 micros ITD, 80 degrees excentricity) and 'near ' (300 micros ITD, 30 degrees ) deviant stimuli (each deviant P=0.075) were presented via headphones. While 15 young healthy subjects passively listened to these sequences, the mismatch negativity (MMN) of the event-related potential was obtained for the deviant sounds. MMN was reliable for all four deviants but larger for the far-lateralized sounds. Moreover, MMN was larger contralateral to the location of the deviant. This indicates a role of preattentive mechanisms in the spatial analysis of auditory scenes.

Adult↗