In order to understand neuronal population activity and to understand how it generates behaviour, the activity of each of the contributing neurons and their interaction must be known. Methods such as EEG, MEG, and fMRI that are regularly used in the cognitive neurosciences do not provide the necessary resolution. The fMRI signal is rather indirectly coupled with the activity of rather large groups of neurons, as it essentially measures signals based on changes in brain blood perfusion that are correlated with neuronal activity, but have completely different spatial and temporal properties. Others, such as EEG and MEG, lack the necessary spatial resolution, as they report the sum of the activity of large populations of neurons. The invasive measurement of signals from single nerve cells in humans is limited to rare occasions in which a well-defined clinical problem, such as the search for the source of a seizure, may require invasive scrutiny of the brain.
Although these spin-offs of therapy-oriented invasive approaches have undoubtedly contributed to our understanding of the human brain, their general applicability is hampered by the indispensable priority of the medical goal, which constrains the time available to do the research. Obviously, the scientist involved is not free to select a target structure of choice, but is restricted to the site to be explored for medical reasons. A final qualification pertains to the fact that the brains studied are those suffering from a disabling disease, processing information in an aberrant manner. Studying single and multineuronal signals in healthy animals is devoid of all these limitations and is the only way to acquire information about information processing by neurons in parts of the brain that usually are not involved in clinical procedures.
For more information about the CIN's use of animals in research, and about the legal, ethical, and scientific ramifications please take a look at the animal research section.
Scientific investigation always works with models that are simple and can be easily understood, or are in other ways advantageous - for instance because they are easily amenable to experimental control and manipulation. Using these models, basic insights can be gained which then lead to a more complete understanding of complex models. This is exactly the role of animal models in life sciences. If a suitable model of a human brain system is chosen, the conclusions suggested by study of the model are in most cases valid for the human system at stake.
Nevertheless, careful consideration is always warranted and investigators will try to test critically the applicability of a concept by formulating through non-invasive experiments that address the human system, designed on the basis of insights derived via animal experimentation. Animal experiments allow the recording of neuronal signals with unrivalled precision. Small arrays of microelectrodes can be introduced to record from several single nerve cells in parallel without destroying tissue. Furthermore, 2 photon imaging is currently developed to measure complex intracellular chemical signals from multiple single nerve cells at the same time.