Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Dopamine leaves its mark in brain scans

21.11.2014

BOLD signals in functional magnetic resonance imaging do not always reflect what nerve cells are doing

Researchers use functional magnetic resonance imaging (fMRI) to identify which areas of the brain are active during specific tasks.


Dopamine alters the so-called BOLD signal in MRI:

Left: If the visual cortex of the brain is active, the BOLD signal increases without dopamine. The activities of gamma waves, individual groups of nerve cells (MUA) as well as the blood flow in the area (CBF) also increase.

Centre: Under the influence of dopamine, the BOLD signal decreases. The gamma-waves and the activity of the nerve cells, however, remain constant. The blood flow even increases.

Right: Active regions (red) in the visual cortex of the brain.

© MPI f. Biological Cybernetics / D. Zaldivar

The method reveals areas of the brain, in which energy use and hence oxygen content of the blood changes, thus indirectly showing which cell-populations are particularly active at a given moment.

Researchers from the Max Planck Institute for Biological Cybernetics in Tübingen now demonstrate that activity induced by signalling molecules such as dopamine may yield hitherto unpredictable up or down modulations of the fMRI signals, with the result that the neural and vascular responses dissociate. In such cases, far more precise data can be obtained when fMRI is combined with concurrent measurements of cerebral blood flow.

When you work hard, you breathe heavily. The same applies to nerve cells. When neurons fire, they consume more oxygen that is being delivered through blood. To ensure that no deficiency occurs, an oversupply of oxygenated blood is immediately transported to active regions of the brain. As a result, the oxygen content of the blood rises in those areas. In a magnetic resonance -scanner, this process is measured in the form of a blood oxygenation level dependent (BOLD) signal. When the activity of nerve cells increases, the BOLD signal increases too - in theory.

However, external influences such as mood, age, drugs, and food can alter BOLD signals and thereby change the interpretation of fMRI results. Moreover, the results are also affected by different brain states such as attention, memory and reward. “There is no absolute correlation between neuronal activity and BOLD signals.

Consequently, our ability to interpret the signals from fMRI scans is limited,” says Daniel Zaldivar of the Max Planck Institute for Biological Cybernetics, describing the motivation starting point of his research. Together with his colleagues, he studied how nerve cells in the visual cortex of macaque monkeys respond to visual stimuli when the brain is simultaneously under the influence of dopamine. The surprising result: although the activity of the nerve cells increases, the BOLD signal decreases by about 50 percent. This can lead the viewer of a brain scan to erroneously conclude that these neurons are less active.

“Dopamine presumably causes active cells to consume more oxygen than can be delivered,” says Zaldivar. Paradoxically, dopamine ramps up neurons’ activity to such a degree that the BOLD signal shows exactly the opposite of what is really happening. Under the influence of dopamine and probably other neuromodulators, changes in the BOLD signal alone are therefore not sufficient to draw conclusions about the activity of neuronal cells.

Measurements of cerebral blood flow in combination with BOLD and neurophysiology offer better insight into the changes of energy metabolism and help to draw better conclusion about the neuronal cells activity. That is because cerebral blood flow provides more direct information about the delivery of oxygen. Interestingly, Zaldivar and colleges found that under the influence of dopamine, blood flow increased. This results lead to the conclusion that the increase along with the neural activity is driven by increased energy use.

"If we can improve our understanding of how BOLD signals change under the influence of neuromodulators, we may be able to interpret brain scans better and detect problems at an earlier stage,” says Zaldivar. In schizophrenia patients, for example, the dopamine system in the brain is poorly regulated. If scientists knew what impact neuromodulators such as dopamine have on brain scan images, it might be possible to diagnose such illnesses earlier. “Before drawing conclusions about neuronal activity from BOLD signals, we first need to know what influence neuromodulators have on the images,” says Zaldivar.


Contact

Prof. Dr. Nikos Logothetis
Max Planck Institute for Biological Cybernetics, Tübingen

Phone: +49 7071 601-651

Email: nikos.logothetis@tuebingen.mpg.de

 
Dr. Daniel Zaldivar
Max Planck Institute for Biological Cybernetics, Tübingen

Phone: +49 7071 601-657

Email: Daniel.Zaldivar@tuebingen.mpg.de

 
Dr. Jozien Goense

Institute of Neuroscience & Psychology
University of Glasgow

Email: Jozien.Goense@glasgow.ac.uk


Original publication
Daniel Zaldivar, Alexander Rauch, Kevin Whittingstall, Nikos K. Logothetis, Jozien Goense

Dopamine-induced dissociation of BOLD and neural activity in macaque visual cortex

Current Biology, 20 November 2014

Prof. Dr. Nikos Logothetis | Max-Planck-Institute

More articles from Life Sciences:

nachricht Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery
20.01.2017 | GSI Helmholtzzentrum für Schwerionenforschung GmbH

nachricht Seeking structure with metagenome sequences
20.01.2017 | DOE/Joint Genome Institute

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>