Annika Tröger-Nietzel

Home Institution
Humboldt-Universität zu Berlin

Host Institution
Laboratory for Magnetic Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston
Research Mentors: Alvaro Pascual-Leone, M.D., Ph.D., Gregor Thut, Ph.D.

E-Mail: annika_nietzel@yahoo.de

Research Topic
see Abstract
Personal Reactions to the U.S. Experience
It was definitely a very valuable experience. I found it reassuring to discover that feeling at home away from home is actually not that hard. Living in Cambridge was very nice. Due to the unbelievable number of colleges, universities and research facilities in the Boston area, the place has a very international feel to it. A friend of mine, for example, shared an apartment with a Japanese, an Israeli and a Norwegian (she herself is from Bulgaria). The threshold for social contacts seemed to be lower than in Germany. You meet people and get party invitations quite easily.
Work in the lab was intense, but really worthwhile. I learned so many new things that I felt a bit dizzy at first. Many things concerning research were easier than in Germany, but I found it quite striking that research and also the healthcare system in the States are so business- and money-oriented (but hence the lack of problems that stem from poor funding). As much as I felt at home, I became very aware of my being European and my different understanding of world politics and nationalism during the debate about a war with Iraq that was going on during my stay.
Greatest Difficulties Encountered
I might repeat some of the things said in previous yearbooks, but then again, this place does not change all that much:
1) the cost of living (Boston is expensive, has that been mentioned before??);
2) riding a bike without facing death;
3) not having a washing machine in the apartment/building. I was running out of clean clothes on a regular basis, because a trip to the laundromat always seemed such a huge project.
Most humorous incident
The morning after one of my roommates had his farewell-party, this was what I saw in the hallway when I stepped out of my room: a huge bucket filled with water and clothes, and nearby, my roommate's girlfriend, wrapped in a blanket and looking quite puzzled, wondering how her jeans got in there. The mystery was never solved.
Helpful Hints for Future Students
- When you're done with your work for the day, leave the lab. I found it difficult sometimes, especially during the first months, since there would always be people staying really long and I would feel like a slacker.
- For cheap and drinkable wine, go to Traders Joes on your way home (several stores in Boston and Cambridge). They have unbeatable prices.

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Abstract on Research Topic
Does lateralization of occipital alpha predict perceptual bias in a spatial cueing paradigm?
Authors
Nietzel, Annika , Thut, Gregor, and Pascual-Leone, Alvaro
Institution
Laboratory for Magnetic Brain Stimulation, Neurology Dept, Beth Israel Deaconess Medical Center, Boston

Purpose
Attention can be covertly oriented toward a location in the visual field without moving the eyes. Such shifts of attention to one side have been related to lateralized changes over the occipital cortex in electroencephalographic (EEG) alpha activity (increase ipsilateral to the attended side, interpreted to reflect active inhibition of unattended space). Covert attention shifts improve the speed and reduce the threshold for detecting stimuli that appear at the locus of attention, at the cost of stimuli located elsewhere in the visual field. We investigated whether an EEG lateralization index, derived from occipital alpha activity, determines this perceptual bias.

Materials and Methods
EEG activity was recorded from 45 scalp electrodes during a spatial detection task. An auditory cue informed the subjects of the location of upcoming lower visual-field targets (flashed for 40 ms), which consisted of black rectangles presented either to the right, the left or bilaterally of a fixation cross. Targets were adjusted to peri-threshold size for each subject. Subjects were asked to perform covert shifts of attention toward the indicated direction (66% probability for stimuli to appear at cued location) and reaction times to targets were recorded.
Alpha (8-14 Hz) power evolution was computed according to the event-related (de)synchronization method, not corrected to a pre-cue reference interval [3]. Lateralization indices were calculated for occipital regions of interest in the cue-target interval according to the following formula: Index = alpha(right occ) - alpha(left occ) /average(left and right occ).
Results
On average, a higher level of alpha-power was observed over the left as compared to the right occipital cortex (Figure: right panels: index always negative), even during the pre-cue period.
Alpha activity for fast vs. slow reaction times: In each individual subject (n=4 to date), stronger lateralization of occipital alpha to the left (index more negative relative to overall left-ward bias) was associated with a more rapid detection of left than right visual field targets, while less pronounced lateralization to the left led to the opposite effect (Target x Speed interaction: p=0.04).
Alpha activity for detected vs. undetected targets: The lateralization index showed no consistent relationship to probability of detection. Instead, there was a lower level of overall occipital alpha for detected stimuli in all subjects (p=0.005).
Conclusion
Our results indicate that perceptual benefits from covert attention shifts are associated with differential modulations of alpha-power over occipital cortex. It is suggested that lateralization of alpha-power can be used for estimation of an attentional vector predicting perceptual bias.