Making Memories

A mashup of memorable mind level research results

I have not published a mind-level neuroscience newsletter in while. Prior related topics are listed in the References, if you’d like to binge on more of this kind of research. But here are a few new findings to peruse.

Learned Motor Patterns Are Replayed in Human Motor
Cortex during Sleep

When learning to jump horses, I would fall asleep and immediately go back to training for the arena course, in my ‘dreams’. Same thing happened with figure skating jumps. Turns out, I was tuning up my motor memory of the techniques involved, while I slumbered away. Replay is a strategy the brain uses to remember new information.

A recent case report from a 36-year-old man with tetraplegia, T11, shows clear evidence for the phenomena happening in humans. Prior mouse experiments looked at maze running. Monitoring devices can show that a specific pattern of neurons will light up as it traverses the correct route. Checking back when the rodent sleeps, those same neurons will fire again in that same order. Is this how the brain allows a memory to be consolidated?

Neural signals for this study were acquired from two microelectrode arrays chronically implanted in left precentral gyrus. A, A three-dimensional reconstruction of the research participants' brain. Blue represents left precentral gyrus. Green and blue squares represent the precise location of the two Utah arrays. B, Spike sorting reveals single-unit and multiunit activity on each array (medial array on the left, lateral array on the right) during the first (top) and second (bottom) recording session. All amplitude plots demonstrate mean ± SD of activity for each threshold crossing event, with color representing event type based on automated sorting algorithm (Vargas-Irwin and Donoghue, 2007). Gray amplitude plots represent multiunit activity. Blue, orange, and yellow amplitude plots represent isolated single-unit activity. There were 78 and 51 single units isolated from the medial array and 12 and 6 single units isolated from the lateral array from Sessions 1 and 2, respectively. The smaller number of single units recorded from the lateral array comports with the finding that activity on the lateral array is typically sparser and less closely associated with task performance.The Journal of Neuroscience (2022). DOI: 10.1523/JNEUROSCI.2074-21.2022

To study whether replay occurs in the human motor cortex, T11 was asked to perform a memory task similar to the electronic game Simon, in which a player observes a pattern of flashing colored lights, then has to recall and reproduce that sequence. He could control the cursor by thinking about moving his own hand. Sensors implanted in T11's motor cortex then measured his patterns of neuronal firing, which reflected his intended hand movement, allowing him to move the cursor around on the screen and click it at his desired locations. Later, while T11 slept, his motor cortex activity was recorded. He, too, played the game in his mind, while sleeping.

T11's patterns of neuronal firing during sleep exactly matched patterns that occurred while he performed the memory-matching game earlier that day. Most of this replay occurred during slow-wave sleep, and was much less likely to be detected while in REM phase.

Overview of experimental paradigm. A, Timeline of the recording sessions. On the second of the two recording dates, we recorded intracortical neural data and surface EEG during the night before the experimental session. Both recording sessions then otherwise began with a brief intracortical/EEG sync routine, followed by the standard calibration routine. B, During the calibration routine, the participant completes a radial-eight center-out task, during which he is cued to move the cursor to 1 of 8 targets surrounding the center starting point. Early in the calibration routine, the error attenuation (EA) (on the accompanying graph) is set close to 1, such that most of the cursor movement is performed automatically. The internal weights of the steady-state Kalman filter are iteratively updated as the EA is reduced in a stepwise fashion and the participant is given full control of the neurally driven cursor. After calibration, the participant then took a 30 min rest during which we recorded both intracortical and surface signals. Following the rest period, the participant engaged in the motor sequence memory task (detailed in C). After 10 blocks of the motor task, the participant took another 30 min rest. We then recorded neural signals overnight as the participant slept. C, The motor sequence memory task. Every trial begins with a sequence demonstration, during which 1 of the 4 colored shapes is sequentially illuminated as a brief auditory tone is played. This sequence is played over 3 s. After the sequence demonstration is complete, a small neurally controlled cursor appears in the middle of the screen. The participant's task is to move the cursor to each of the 4 shapes in the same sequence as was just demonstrated. The participant completed 10 blocks of 16 trials on each recording session day. On each recording session day, there was one “target” sequence (which was different between the two sessions). In each block, 12 of the 16 trials were of the target sequence, and the other 4 trials were randomly generated “distractor” sequences. The Journal of Neuroscience (2022). DOI: 10.1523/JNEUROSCI.2074-21.2022

Memory-enhancing properties of sleep actually depend on the oscillatory amplitude of the stress hormone, norepinephrine (NE)

We know that memory consolidation occurs during sleep. Lessons learned need to be slept on. But what about all that tossing and turning and waking up all night long. That messes up the process, right? No, all that is necessary. Norepinephrine causes you to wake up more than 100 times a night. And that is during perfectly normal sleep.

Sleep has a complex micro-architecture, encompassing micro-arousals, sleep spindles and transitions between sleep stages. Fragmented sleep impairs memory consolidation, whereas spindle-rich and delta-rich non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep promote it. However, the relationship between micro-arousals and memory-promoting aspects of sleep remains unclear. In this study, we used fiber photometry in mice to examine how release of the arousal mediator norepinephrine (NE) shapes sleep micro-architecture. Here we show that micro-arousals are generated in a periodic pattern during NREM sleep, riding on the peak of locus-coeruleus-generated infraslow oscillations of extracellular NE, whereas descending phases of NE oscillations drive spindles. The amplitude of NE oscillations is crucial for shaping sleep micro-architecture related to memory performance: prolonged descent of NE promotes spindle-enriched intermediate state and REM sleep but also associates with awakenings, whereas shorter NE descents uphold NREM sleep and micro-arousals. - C Kjaerby et al.

ISOLATION STRESS EFFECT on MEMORY— DARK CHOCOLATE to the RESCUE

All alone under Lockdowns and Quarantines? What is your go to food source for solace? Dark Chocolate, of course. And now there is science to back you up on that. It can reverse bad brain effects and … no weight gain!

A recent rat study investigated the impact of different dark chocolate (DC) dietary eating patterns on the synapses in the hippocampal CA1 area, in particular synaptic potency and plasticity. These 35 rats, divided into five groups of 7, each ate dark chocolate while experiencing chronic isolation stress. Each group following a different dietary pattern. The three dark chocolate dietary patterns they tested were dubbed stress-compulsory [only received DC], stress-optional [received unlimited chow and/or DC] and stress-restricted [chow freely and only 4 g DC daily].

Then the slope and amplitude of field excitatory postsynaptic potentials (fEPSPs) were assessed based on the Input-Output (I/O) curves and after the longterm potentiation (LTP). The fEPSP slope and amplitude in the I/O curves and after LTP decreased in the stress groups, compared to the control groups. These parameters changed significantly in both compulsory and restricted DC dietary patterns, compared to the stress group. All the dark chocolate dietary patterns showed reduced food intake and their body weight, especially the compulsory and restricted dietary patterns.

Well must say bye for now. I’m off to take a nap, after first munching some Hershey’s - gotta perfect that tennis serve!

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REFERENCES

DB. Rubin et al, Learned Motor Patterns Are Replayed in Human Motor Cortex during Sleep, The Journal of Neuroscience (2022). DOI: 10.1523/JNEUROSCI.2074-21.2022

C Kjaerby et al. Memory-enhancing properties of sleep depend on the oscillatory amplitude of norepinephrine. Nature Neuroscience (2022). DOI: 10.1038/s41593-022-01102-9

E Kalantarzadeh et al. The impact of different dark chocolate dietary patterns on synaptic potency and plasticity in the hippocampal CA1 area of the rats under chronic isolation stress. Nutritional Neuroscience (2022). DOI: 10.1080/1028415X.2022.2088946

Related past newsletters:

https://biomedworks.substack.com/p/energy-efficient-brain-intelligence

https://biomedworks.substack.com/p/spirituality-found-in-brain-area

https://biomedworks.substack.com/p/brain-gateways

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