APPROACHES AND OPPORTUNITIES IN NEUROSCIENTIFIC RESEARCH USING WIDE-FIELD IMAGING
In recent years, technological advancements and access to wide-field (“mesoscopic” or “macroscopic”) imaging technology have significantly transformed our understanding of brain function. Referring to the significance of data acquisition at this scale, Angela Nietz and her collaborators wrote (in their 2022 Biology review paper Wide-Field Calcium Imaging of Neuronal Network Dynamics In Vivo): “In physical systems, new properties emerge at the macroscopic level that are not observable at smaller scales. At the macroscopic level, temperature, viscosity, and density are the collective properties of the statistical motions of the atoms and molecules of gases and fluids, not of the individual particles. Magnetism and conductivity do not exist at the atomic level, instead emerging from the interactions among individual atoms (technically these are examples of weak emergence). Similarly, in the nervous system, it is the interactions among populations of neurons that underlies the neural representations of perception, behavior, and brain states. Therefore, understanding neuronal dynamics at the mesoscale is of fundamental importance”
This year, 2024, kicked off with another excellent Neurophotonics wide-field imaging review by Ariel Gilad, focusing specifically on the value of mesoscopic/macroscopic imaging in studying cognition in mice, also reviewing recent technical advances in the field, as well as referring to some research highlights from landmark studies implementing the technique in the years predating the review. These studies illustrate the versatility and power of wide-field microscopes/macroscopes in examining complex neural dynamics and interactions. He also discusses some of the benefits and limitations and suggests future directions this technology might take.
Since the publication of this review at the start of this year, dozens of research papers have seen the light in peer-reviewed journals or as preprints, where using a wide-field imaging microscope (“macroscope/mesoscope” also seem to be interchangeably used) was a key to unlock their research questions, or where it even was the lead character in the plot of the paper. In this blog post, we very briefly dip into a dozen of these papers, pointing out common approaches and opportunities for using this technology in neuroscience research.
Whilst this is by no means a comprehensive overview, we hope for this format to trigger some ideas in the mind of the reader, maybe contributing in a small way to the scope of a future research project. And we hope to give a taste of the vast scope of valuable research questions that can be investigated at the network level, using this relatively inexpensive, user-friendly method. It opens a different paradigm in neuroscience for investigation.
With this aim and focus, some of the general themes in these 2024 papers are:
- Using novel targets for expressing genetic fluorescence reporters. [1, 2, 3]
- The use of newly developed calcium and voltage indicators, displaying altered characteristics that enable the study. [2, 3]
- Combining mesoscopic/macroscopic imaging with other recording techniques and a variety of behavioural paradigms. [1, 2, 3, 5, 6, 7, 8, 10, 11]
- Designing new data analysis methods. [4, 5, 12]
- Investigating network effects in altered states of consciousness or altered brain function due to injury or disease states. [3, 4, 5, 6, 7]
- Since the technique is relatively non-invasive, it allows for long-term recordings. This is particularly interesting for groups that focus on learning and development. [6, 8]
- Because of its systems- or network approach, there are interesting implications for applied research in brain-machine interfaces and machine learning. [5]
- The method and integration with other methods generate huge and complex data sets. This offers the opportunity to apply machine learning methods to data analysis, in real-time and post-acquisition. [5, 12]
- Since the technique can be applied to so many questions, some papers focus specifically on developing wide-field imaging mesoscope/macroscope technology [10, 11]
2024 Wide-field Imaging/Mesoscope/Macroscope Research Papers
In the first of the 2024 papers on our list, Cell class-specific long-range axonal projections of neurons in mouse whisker-related somatosensory cortices [1], researchers combined mesoscopic data, optogenetic stimulation and a behavioural setup with light-sheet imaging to visualize GCaMP signals expressed in specific neuronal -sub/types. This was done to construct functional and anatomical connectivity maps of the neural network involved in sensory processing. Similarly, Visual stimulation drives retinotopic acetylcholine release in the mouse visual cortex [2] showcased the selective expression of reporters investigate specific neurotransmitter function in visual cortex, and how wide-field imaging can be used to map neurotransmitter dynamics in response to sensory stimuli.
Cortical Networks Relating to Arousal Are Differentially Coupled to Neural Activity and Hemodynamics [3] highlighted the dual use of wide-field microscopy with electrophysiology, exploring how arousal states affect neural and vascular responses in cortical networks. Using a novel voltage-sensitive reporter, the study found positive correlation of arousal state with global hemodynamic changes in some cortical areas, with a slight negative correlation in others.
Another pivotal study, Group ICA of wide-field calcium imaging data reveals the retrosplenial cortex as a major contributor to cortical activity during anesthesia [4], employed wide-field imaging and Independent Component Analysis (ICA) to uncover the roles of various brain regions during altered states of consciousness. This study also emphasizes the significance of different brain states and its influence on synchronous activity in the different brain areas. Moreover, Attention-Based CNN-BiLSTM for Sleep State Classification [5], illustrated how machine learning techniques can be used to classify neural patterns, integrating behavioural data with wide-field imaging data to investigate neuroplasticity during different sleep states.
Similarly, a preprint from Rutgers researchers demonstrated the impact of altered brain states on network activity, but this time caused by focal traumatic brain injury (Imaging the large-scale and cellular response to focal traumatic brain injury in mouse neocortex [6] ). They used macroscopic/mesoscopic imaging combined with two-photon microscopy and electrophysiology, providing a comprehensive view of cellular and network responses, how it develops post-injury and how it relates to behaviour.
These studies, along with others like Mapping brain state-dependent sensory responses across the mouse cortex [7] demonstrate wide-field imaging technology’s value in investigating neural activity across various states and conditions. It also offers valuable insights into neurovascular coupling with neural activity. Furthermore, it shows how useful it is to combine it with other methods to understand multi-scale dynamics, linking these insights with behavior.
In another preprint, this time from Berlin, they investigated decision-making with an interesting novel behavioural paradigm [The neural mechanisms of fast versus slow decision-making [8]). The group showcased mesoscopic imaging’s value in revealing large-scale cortical patterns during decision-making processes, integrating optogenetic control and electrophysiological data with the wide-field imaging data.
Focus on the further development of mesoscopic or macroscopic imaging technology is itself a popular research topic. It offers fertile grounds for further technical innovation, not only in data analysis but also on the acquisition front:
In a study led by Mark Howe’s group in Boston, they demonstrate a method for imaging from typically inaccessible deep-tissue areas, combining wide-field microscope with implanted micro-fiber array [Targeted micro-fiber arrays for measuring and manipulating localized multi-scale neural dynamics [10]), combining it with optogenetic manipulation of these areas. In The June-edition of Neurophotonics, another technical innovation is reported in Widefield in vivo imaging system with two fluorescence and two reflectance channels [11]. The paper explains how they simultaneous monitored neural activity and hemodynamics using a colour multiplexing protocol. The ability to combine different wide-field imaging measurements with other techniques offer exciting possibilities for understanding complex brain dynamics.
And finally, still in the scope of technology development, but with a different angle in terms of its field of application: Operant conditioning of cortical waves through a brain-machine interface [12] demonstrates the value of using mesoscopic imaging data as a tool for brain-machine interface development.
Wide-field imaging’s multifaceted applications and synergies with other developing technologies open many new avenues for understanding the complexities of neural networks and its implications for behavior and cognition. Have you come across other interesting approaches where wide-field imaging macro/mesoscopes were used in neuroscience? Please add a link below in the comments section – we’ll update this blog to include the latest developments. Also make sure to read the next article in this blog series, about likely future developments that would likely further improve the usefulness of wide-field imaging to the neuroscience community.
