In a research article in Science in June of this year, readings from implanted electrodes showed that the medial frontal cortex accesses memory when it needs to in order to make a decision.
‘Flexibly switching between different tasks is a fundamental human cognitive ability that allows us to make selective use of only the information needed for a given decision. Minxha et al. used single-neuron recordings from patients to understand how the human brain retrieves memories on demand when needed for making a decision and how retrieved memories are dynamically routed in the brain from the temporal to the frontal lobe. When memory was not needed, only medial frontal cortex neural activity was correlated with the task. However, when outcome choices required memory retrieval, frontal cortex neurons were phase-locked to field potentials recorded in the medial temporal lobe. Therefore, depending on demands of the task, neurons in different regions can flexibly engage and disengage their activity patterns.’
In my book How the Brain Thinks I discuss how the frontal lobe, with its associated cortex and underlying connections, has evolved to be the largest lobe of our brain. The important prefrontal cortex covers the front of this lobe and is involved in performing higher-order, executive-level functions in the brain.
The prefrontal cortex has three interrelated abilities that provide some of the support for these higher-order activities, including flexible, complex thinking:
• The ability to hold on to and work on information over a period of time • working-memory
• Prolonged and focused attention.
Amongst other things, these features:
• Help us to produce our own personal narrative, rumination, our default mode network, and assists in producing and maintaining consciousness
• Allow us to produce abstract thoughts
• Enable us to plan and perform our complicated social functions, a process called executive control.
The prefrontal cortex helps to process information using either simple emotion or more complex cognition, empowering us to think both fast and slow. It is also largely responsible for our personality and intelligence.
Anatomically, the prefrontal cortex makes up thirty per cent of the total cortex and lies in the front of, or rostral to, the rest of the brain, merging with other cortical areas behind it in the frontal lobe with little clear-cut separation. There is still an ongoing debate about the precise definition of what the prefrontal cortex is and does and what separates it from other cortical areas.
Broadly speaking, the prefrontal cortex can be divided into medial and lateral areas, along with areas underneath (ventral) and on top (dorsal, think dorsal fin of a shark). These areas include the dorsolateral prefrontal cortex (DLPFC), the dorsomedial prefrontal cortex (DMPFC), the ventromedial prefrontal cortex (VMPFC), and the orbitofrontal cortex (OFC).
Lying underneath the medial side of the prefrontal cortex, the VMPFC is heavily connected with the amygdala, a nucleus in the temporal lobe that has an important role in both fast and slow emotional processing. It is also close to and well connected with the cingulate cortex that curves around and in front of the corpus callosum on the medial side of the cerebral hemispheres, and plays an active role in both fast and slow decision making.
Some authors include the anterior portion of the cingulate cortex (ACC) in their definition of the VMPFC because some features of the ACC are similar to the prefrontal cortex.
In patients with medial frontal lobe damage affecting the VMPFC, their outward behaviour appears normal and they perform well in intelligence tests. But their day-to-day functioning is affected and their social behaviour is inappropriate, showing little inhibition and a lack of moral judgement.
Thinking is done in context, and culture is an important part of that context. The values and standards that are ingrained within our cultures are a huge influence on our thinking. With its ready access to memory and emotion, the VMPFC may help us use these standards to assess the repercussions of our own behaviour and decide how to behave appropriately within the cultural context. It can also help us in our moral judgements, as our cultural beliefs define our morality.
Some patients with frontal lobe lesions and limited executive control can exhibit other unusual behaviours. Normally, when we are confronted with new information, we take a moment to process it and to think about its relevance in the context using our frontal cortex, particularly our VMPFC, to access memory and emotion. Lhermitte showed that patients with frontal lobe lesions involving the VMPFC are excessively dependent on instant cues. In these patients, just seeing an object compels them to do something with it, without the overall context being taken into account. These patients also commonly imitate inappropriate behaviours of other people.
Memory is gained from experience and acts as an information bank with which to compare current cues, to determine relevance. We can’t suddenly respond to everything we come across, picking up everything we see or imitating everyone else’s behaviour. It could be dangerous and very time-consuming.
What if there were many objects and one of them was hot, or the behaviour we had seen was socially unacceptable? What would happen then, if we had no control?
This article in Science consolidates our knowledge of the connections between the medial frontal and pre-frontal cortex and the areas of the medial cerebral cortex concerned with memory and decision making.
Until next time.
