40Hz – Title of the Website

I have chosen „40Hz“ as the title of this website since it happens to be the nickname for one of the experimental

phenomena I am interested in, namely, fast neuronal oscillations in the so-called gamma-range. Although gamma

oscillations can be observed anywhere in a broad frequency band between 30 and 100Hz, they are often found to

occur prominently around 40-50Hz. This holds specifically for many human EEG experiments – hence the label

„40Hz“.

References

The physiology of gamma-band oscillations is reviewed in a number of papers:

1. • König P, Engel AK, Singer W (1995) The relation between oscillatory activity and long-range synchronization in
   

2. cat visual cortex. Proceedings of the National Academy of Sciences USA 92: 290-294 (pdf)
   

3. • Tallon-Baudry C, Bertrand O (1999) Oscillatory gamma activity in humans and its role in object representation.
   

4. Trends in Cognitive Sciences 3: 151-162 (pdf)
   

5. • Singer W (1999) Neuronal Synchrony: A Versatile Code for the Definition of Relations? Neuron 24: 49–65 (pdf)
   

6. • Fell J, Fernandez G, Klaver P, Elger CE, Fries P (2003) Is synchronized neuronal gamma activity relevant for
   

7. selective attention? Brain Research Reviews 42 (2003) 265–272 (pdf)
   

8. • Herrmann CS, Munk MHJ, Engel AK (2004) Cognitive functions of gamma-band activity: memory match and
   

9. utilization. Trends in Cognitive Sciences 8: 347-355 (pdf)
   

10. • Fries P (2005) A mechanism for cognitive dynamics: neuronal communication through neuronal coherence.
    

11. Trends in Cognitive Sciences 9: 474-480 (pdf)

Gamma oscillations

Correlated firing of cells occurs in a large number of different neural systems and across a wide range of species. It

has been observed in all sensory systems, in the motor system and in memory/association structures. The species

include primates, carnivores, lagomorphs, rodents, birds, reptiles, amphibia and insects. In many of these studies

that have analysed correlated neural activity, synchrony between separate neurons has been found in association

with gamma-band (>30Hz) oscillations. Similar evidence is available for the human brain. Early studies have

demonstrated gamma-band activity in the auditory cortex. Subsequently, gamma frequency components have

been studied in visual and language processing and during the execution of motor tasks. There is a continuing

evolution of the methodologies employed for quantifying gamma-band effects. While the earliest studies measured

classical event-related potentials (ERPs) filtered in the frequency bands of interest, later investigations have

focussed on the temporal variation of spectral power after stimulus presentation. Most recently, wavelet-based

methods for analysing spectral power and coherence across recording sites have been introduced. Whereas the

classical ERP approach, by definition, captures only the signal components which are phase-locked to the external

event, these more recent techniques permit the distinction between phase-locked and non-phase-locked (so-called

„induced“) components. What the available studies demonstrate is the occurrence of gamma activity under a wide

variety of tasks and paradigms including processing of coherent stimuli, perceptual discrimination, focussed

attention, short-term memory, sensorimotor integration, and language processing. Typically, the observed amount

of gamma is positively correlated with increased „processing load“ and, thus, with the level of attention, as well as

with the difficulty or integrative nature of the processing. Generally, the human data are in good agreement with

the animal studies suggesting a role of gamma synchronization in the binding and selection of distributed

information.