The Impact of Environment-Gene Interaction on Brain Development

Post by Elisa Guma

What did we learn?

Brain development is a highly orchestrated, complex process driven by genetic background and its interaction with the environment, which can exert both positive and negative influences on development. For example, exposure to an enriched environment promotes the development of healthy brain circuits. Furthermore, environmental enrichment has been shown to help aid in the production of new neurons (neurogenesis) in the hippocampus, which may buffer against age-related cognitive decline. Recent evidence suggests that environmental enrichment may be exerting these positive effects by inducing epigenetic changes in the DNA of hippocampal neurons. More specifically, it can reverse the negative effects of aging on DNA methylation in neurons of the hippocampal dentate gyrus involved in neuroplasticity and neurogenesis, critical for learning and memory (see Zocher and colleagues).

Unfortunately, environmental exposures may also disrupt neurodevelopment, which may, in turn, increase the risk of developing psychiatric illness. These negative effects may be particularly heightened if coupled with genetic risk. Just as the hippocampus has been found to be sensitive to positive environmental pressures, it is also susceptible to negative influences. Recent evidence by Song and colleagues has shown that exposure to both a genetic risk factor (risk gene for schizophrenia, DISC1) and an environmental risk factor (in utero exposure to maternal infection) can disrupt the structural and functional development of projections from the hippocampus to the prefrontal cortex in early development. This pathway may underlie many of the cognitive deficits associated with psychiatric illness.

What's next?

Our genes and the environment we are exposed to act in concert to shape our brain and behavioral development. Understanding how these factors interact during specific developmental windows could help us identify how and when to intervene during a child’s development. Identifying potential environmental interventions to buffer against both environmental and genetic risk factors for psychiatric illness will be an interesting avenue for future research in 2022.

A Better Understanding of Memory Formation and Storage

Post by Shireen Parimoo

What did we learn?

The hippocampus is central to memory formation and retrieval as it receives and integrates information from across the brain. Memory for associations or episodic information (such as an event consisting of location, people, and time information) are particularly reliant on the hippocampus as it is thought to bind the different elements of an event together into a single representation. The formation and retrieval of memories are supported by the structure and function of the hippocampus and its interactions with the neocortex.

2021 only further advanced our understanding of the hippcampus’ pivotal role in how memories are formed and accessed. During memory encoding, Griffiths and colleagues showed that oscillatory activity within the hippocampus was related to better associative memory. Specifically, greater theta-gamma coupling during mnemonic binding predicted better memory for associations (e.g., a pattern and an item), while memory for single items was related to alpha/beta activity in the occipital cortex during stimulus perception. Gava and colleagues found that individual elements of associative events (e.g., location) are represented by different firing patterns in the same set of co-active hippocampal neurons and demonstrated how these representations are updated across repeated and novel experiences. Relatedly, Gonzalez and colleagues reported that dopamine receptors in the hippocampal CA1 subregion are not involved in retrieving an already-formed memory, but they are important for the consolidation and reconsolidation (i.e. a process whereby memories are reactivated, changed, and restabilized) of new memories. Memory reconsolidation is especially important for schema creation, as it allows information to be linked together across different memories to form a generalized representation of a concept (e.g., the concept of an “office”).

Hippocampal interaction with other brain regions is also important for storing and retrieving memories, particularly newer memories. During retrieval of autobiographical memories, for example, Gilmore and colleagues observed that activity in the posterior hippocampus was selective for recent compared to remote memories. The hippocampus also had greater functional connectivity with cortical regions during recall of recent memories rather than remote memories, further illustrating its differential involvement in temporally graded retrieval. Together, these studies highlight the diversity of hippocampal involvement across different stages of memory formation and retrieval, ranging from encoding and reconsolidation to temporally graded retrieval of autobiographical memories.

What's next?

As a field, cognitive neuroscience is getting increasingly closer to mapping out the neural mechanisms underlying memory formation and retrieval. We currently have some of the puzzle pieces showing how different anatomical brain regions or distinct brain circuits play a role in memory formation and retrieval. These seemingly disparate findings create exciting possibilities for future research to demonstrate how these pieces interact with each other to provide a more comprehensive picture of how the brain forms and stores memories.

How We Perceive Time

Post by Leanna Kalinowski

What did we learn?

The hippocampus has long been considered important for regulating memory of elapsed time. Research in 2021 further advanced our knowledge of the mechanisms underlying this process. For example, Reddy and colleagues identified a role of hippocampal time cells in the human brain, demonstrating the capacity of these cells to store sensory information in a sequential fashion in the presence or absence of a stimulus. Another group of researchers, Dias and colleagues, uncovered how connections between the hippocampus and other brain regions regulate time perception. Specifically, they found that neurons in the medial entorhinal cortex play an important role in reproducing memorized time intervals and passing that information along to the hippocampus.

What's next?

This research paves the way in better understanding how (1) the brain measures and perceives time and (2) how this time perception is incorporated into our memory. Future research in 2022 and beyond is anticipated to further expand our understanding of the brain circuits involved in time perception.