Sitename

 

40 Hz – Title of the Website

I have chosen „40Hz“ as the name 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“.

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.

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

  2. •Tallon-Baudry C, Bertrand O (1999) Oscillatory gamma activity in humans and its role in object representation. Trends in Cognitive Sciences 3: 151-162 (pdf)

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

  4. •Fell J, Fernandez G, Klaver P, Elger CE, Fries P (2003) Is synchronized neuronal gamma activity relevant for selective attention? Brain Research Reviews 42 (2003) 265–272 (pdf)

  5. •Herrmann CS, Munk MHJ, Engel AK (2004) Cognitive functions of gamma-band activity: memory match and utilization. Trends in Cognitive Sciences 8: 347-355 (pdf)

  6. •Fries P (2005) A mechanism for cognitive dynamics: neuronal communication through neuronal coherence. Trends in Cognitive Sciences 9: 474-480 (pdf)