But why not just do EEG?
Electrical brain activity gets too impeded and distorted by intervening tissue layers. Biomagnetic fields, on the other hand, are minimally distorted, allowing us to take advantage of the same trick that gives adult MEG higher spatial resolution than EEG. Genuine fetal EEG requires electrodes attached to the fetal head after the amniotic membranes rupture.
How early can you record fetal brain activity?
Most of our recordings take place in the third trimester (28 weeks’ gestation or later). The cortex isn’t driven by the thalamus until 24–26 weeks, when thalamocortical synapses are formed. Before that point, we can’t record any useful signal.
How many sensors does your system have?
The system in Little Rock is built with 150 axial gradiometers, and the system in Tübingen is very similar, with 156 axial gradiometers. Both systems were designed and manufactured by CTF and are referred to as SARA (SQUID Array for Reproductive Assessment) devices.
I see a lot of published fetal MEG studies using elementary stimuli, like auditory pure tones and flashes of red light. Has anyone investigated if and how the fetal human brain responds to more complex stimuli?
The EU-funded FETAL-MIND project at the University of Tübingen is currently investigating exactly that question. This will be the first project to look at fetal MEG responses to speech stimuli and even face-like light patterns projected into the womb. Also, note that even prior studies that used fairly simple stimuli often had quite sophisticated experimental designs. For instance, work by Julia Moser and colleagues used an auditory local–global task, with oddball deviants both within and between sequences, to study hierarchical learning in fetuses, with results that were suggestive of working memory (and, by extension, perhaps consciousness). An earlier study by Franziska Schleger and colleagues also looked at numerosity detection using auditory tones, demonstrating that fetuses can distinguish sequences containing different numbers of tones.
Can you measure neural complexity/entropy with fetal MEG?
Yes! In one of our most recent studies by Joel Frohlich and colleagues, published in Nature Mental Health (see publications below), we found that the entropy of auditory evoked responses decreases with gestational age. This is likely because, as the fetal brain matures, it converges on a stereotyped cortical response to a stimulus (think about canalization), whereas early in development, these cortical circuits haven’t been as sculpted by maturational processes, so they have noisier responses. This effect also interacts with biological sex, though we are still trying to understand that observation.
Read the paper: Frohlich et al., Nature Mental Health, 2024.
If there are only two sites for fetal SQUID-MEG in the world, how will you replicate findings? Is this work very reproducible?
While there are indeed only two sites globally with specially manufactured SARA devices for fetal MEG, optically pumped magnetometers (OPMs) might soon change the landscape. OPMs are a new, non-cryogenic magnetometer technology. OPM-MEG is less expensive than SQUID-MEG and, moreover, they are portable and can be flexibly deployed, unlike SQUIDs, which are fixed inside a cryogenic dewar. It’s still uncertain whether OPMs will be sensitive enough to work for fetal applications, but if so, they will unlock the world of fetal MEG for many new labs around the world. The ERC project FETAL-MIND at the University of Tübingen will directly compare SQUID-MEG and OPM-MEG for fetal recordings to answer this question. More generally, we hope OPM-MEG will make all forms of MEG (including infant, child, and adult applications) more accessible worldwide, especially in the global south.
Figure 1 from Frohlich et al., NeuroImage, 2023, artwork by Katrin Sippel.
Can you study functional connectivity with fetal MEG?
We get this question a lot. As conventionally measured, no, we cannot look at, say, frontoparietal connectivity with fetal MEG, because the fetal head is always positioned differently in recordings from each pregnant volunteer. We cannot control the position of the fetal head, so each channel is picking up something different in each recording. Moreover, the fetal head is small in relation to the whole sensor array, which is built to cover the entire maternal abdomen. This means just a cluster of maybe 10 channels pick up signals from the fetal brain, and often we average these channels in addition to averaging across trials to improve SNR. For similar reasons, source localization is not practical either.
Can I get involved in fetal MEG research? Do you have any open positions?
We will post any positions on this page. In the meantime, feel free to contact us at fetalmeg@pm.me.
Are there any lectures about fetal MEG I can watch online?
Yes, we recommend starting with these: