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Youngson Cho, MD, PhD: Motivation improves working memory by shaping neural signals in the prefrontal and parietal cortex

December 01, 2020

Youngson Cho, MD, PhD: Motivation improves working memory by shaping neural signals in the prefrontal and parietal cortex

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  • 00:00Hi, I'm young sunshine.
  • 00:02I'm an assistant professor in
  • 00:03the Yell Child Study Center and
  • 00:06in the Department of Psychiatry.
  • 00:08So my talk is entitled motivation
  • 00:10improves working memory by
  • 00:11shaping neural signals in the
  • 00:12prefrontal and parietal cortex.
  • 00:14And as you see,
  • 00:15there's a pretty big carrot
  • 00:16on the slide which I placed to
  • 00:18symbolize incentives or those
  • 00:19things broadly that motivate us.
  • 00:21And my talk will focus on
  • 00:23motivation and how motivation,
  • 00:24effects cognition as a means of
  • 00:27achieving goals.
  • 00:27So to achieve goals,
  • 00:28one must have both the
  • 00:30desire to achieve a goal,
  • 00:31which is the motivation and
  • 00:33the means to achieve the goal,
  • 00:34which here is the ability to
  • 00:36draw on cognitive resources,
  • 00:37and the overarching question in our work
  • 00:39is how do these domains affect each other?
  • 00:43So what is motivation?
  • 00:44I think of it as a drive that helps
  • 00:46organize our desires and efforts
  • 00:48towards goal directed behaviors.
  • 00:50And here we will specifically talk
  • 00:52about incentive motivation or the
  • 00:54motivation that is initiated by incentives.
  • 00:56Theories of incentive motivation.
  • 00:57By Kent Berridge and others suggest
  • 01:00that two things have to come
  • 01:01together for people to be motivated.
  • 01:03External cues signaling incentives
  • 01:04such as food or money,
  • 01:05etc.
  • 01:06And an internal physiological state that
  • 01:07is conducive to integrating these cues,
  • 01:09such as hunger or thirst.
  • 01:11So as a concrete example,
  • 01:12here's a child with ice cream in
  • 01:14the ice cream Services Visual,
  • 01:16an likely olfactory cue,
  • 01:17and he said previous experiences with
  • 01:20ice cream and just by seeing it can
  • 01:22have an internal representation of
  • 01:23ice cream and have an idea of what
  • 01:25it would be like to taste in the near future.
  • 01:29This creates a motivation
  • 01:30to obtain the ice cream,
  • 01:32or in his case,
  • 01:33motivation to sit still and wait
  • 01:35for the ice cream and motivation in
  • 01:38the broadest sense is disrupted.
  • 01:40In many psychiatric illnesses,
  • 01:41including but not limited to schizophrenia,
  • 01:43depression, substance use,
  • 01:44and it's a challenge to know in
  • 01:47which ways motivation is disrupted
  • 01:48and exactly how this disruption
  • 01:50relates to symptoms,
  • 01:51which is a large part of our work.
  • 01:55Motivation does not occur in isolation.
  • 01:57By definition,
  • 01:58motivation must affect other processes.
  • 02:00So in our work we focus on
  • 02:02how motivation affects the
  • 02:04downstream process of cognition.
  • 02:06We specifically focus on working memory,
  • 02:08which is defined as the temporary
  • 02:10maintenance and manipulation of
  • 02:11information in the service of a goal.
  • 02:13Working memory is important
  • 02:14because it serves as a building
  • 02:16block of higher order cognition.
  • 02:18It's required for abstraction
  • 02:20and problem solving.
  • 02:21So examples of working memory
  • 02:23include being verbally told,
  • 02:24a phone number,
  • 02:25and having to keep it in mind
  • 02:27before being able to jot it down.
  • 02:30Calculating a tip at a restaurant
  • 02:32arithmetic requires working memory,
  • 02:33keeping in mind a set of directions
  • 02:35when traveling to a destination.
  • 02:37Prior work has noted that working memory
  • 02:39engages a number of prefrontal cortex
  • 02:41and parietal cortex brain regions.
  • 02:43Here shown in orange,
  • 02:45red,
  • 02:45and pink,
  • 02:46including the dorsal
  • 02:47lateral prefrontal cortex,
  • 02:48the pre Motors cortex and
  • 02:50areas the intraparietal sulcus.
  • 02:51Working memory also improves
  • 02:53throughout childhood and adolescence,
  • 02:55likely paralleling the ongoing
  • 02:57development of the prefrontal cortex.
  • 02:59This ongoing development means that
  • 03:01working memory is dynamic in development,
  • 03:03but also vulnerable.
  • 03:06So how do we achieve our task
  • 03:08of understanding the effects of
  • 03:10incentives on working memory?
  • 03:11We drew from classic working memory
  • 03:13tasks that have been critical for
  • 03:15understanding of how individual
  • 03:16neurons behave during working memory.
  • 03:18However, these tests are typically
  • 03:20used in nonhuman primates,
  • 03:21so we translated this task to
  • 03:23use it in human studies.
  • 03:26The basic premise of this task involves
  • 03:28an encoding period where spatial
  • 03:29location is skewed by yellow circle.
  • 03:31The delay period during which the
  • 03:33yellow circle is disappeared and
  • 03:35the participant has to maintain the
  • 03:36location they previously saw the
  • 03:38probe period in which a participant
  • 03:39uses a joystick to move the Gray
  • 03:42circle to indicate where they saw
  • 03:43the yellow circle and what we care
  • 03:45about is how closely they place
  • 03:47that Gray probe circle to wear.
  • 03:49The yellow circle was initially
  • 03:50the closer the placement,
  • 03:51the better the working memory,
  • 03:53and here we call these working
  • 03:55memory trials neutral trials.
  • 03:56Since there's no incentive linked here.
  • 03:59And in our version of the task we also
  • 04:01have a control condition in which
  • 04:02there is no working memory required.
  • 04:04We call this the motor condition and
  • 04:06hear the yellow circle reappears during
  • 04:08the probe phase and participants
  • 04:10simply move the Gray circle on
  • 04:11top of the yellow circle.
  • 04:13We then manipulated the tasks
  • 04:14such that on some trials you can
  • 04:16win or lose money depending on
  • 04:17your working memory performance,
  • 04:19the better the working memory performance,
  • 04:20the more money one and the worse
  • 04:22the working memory performance,
  • 04:23the more money lost.
  • 04:24So in these types of trials there
  • 04:27is feedback given about how much
  • 04:29money is won or lost.
  • 04:30And we named this task meant tag
  • 04:32which stands for motivational
  • 04:33interactions with cognition.
  • 04:35We use this task with functional
  • 04:37magnetic resonance imaging or fMRI,
  • 04:38and in a group of healthy young
  • 04:40adults and all imaging, acquisition,
  • 04:42and processing was in line with
  • 04:45pipelines from the Human Connectome Project.
  • 04:48The first thing that we noted was that
  • 04:50working memory improves when there
  • 04:52is the possibility of monetary gain or loss,
  • 04:54and throughout the talk the color
  • 04:56red will indicate working memory
  • 04:57trials with monetary loss.
  • 04:59The color green will indicate working
  • 05:00memory trials with monetary gain,
  • 05:02and yellow or neutral working
  • 05:03memory trials without any money
  • 05:05at stake on the Y axis is the main
  • 05:07angular difference between where
  • 05:08the location was kyoudan where the
  • 05:10probe circle was placed.
  • 05:12In the smaller the distance,
  • 05:13the better the working memory and
  • 05:15we see that the gain and loss trials
  • 05:18have better working memory performance
  • 05:20compared to the neutral working
  • 05:22memory condition shown in yellow.
  • 05:23We next tested where in the brain
  • 05:25integrates working memory with
  • 05:27incentives and so that brain regions
  • 05:28that are involved in both working memory,
  • 05:30an incentivized working memory are located
  • 05:32in prefrontal and parietal cortices,
  • 05:34and when we look at the bold signal or
  • 05:36the neural signal within these regions,
  • 05:38we see that these regions have greater neural
  • 05:40signal when working memory is incentivized.
  • 05:42So this is true for both monetary
  • 05:44reward which is shown in green and
  • 05:46monetary loss which is shown in red.
  • 05:48Each of these, the green lines and
  • 05:50the green bars and the red lines
  • 05:52in the red bars rides above the
  • 05:54neutral working memory condition.
  • 05:55And yellow, so these posterior parietal
  • 05:58and prefrontal regions both support
  • 06:01working memory and have greater bold
  • 06:03signal during incentivized working memory.
  • 06:06Next, we wondered whether greater
  • 06:08neural signal could actually be linked
  • 06:10to better working memory performance.
  • 06:12And we observed areas shown in blue that
  • 06:14specifically had greater neural signal when
  • 06:16working memory performance was better.
  • 06:17These were a subset of the regions we saw
  • 06:20earlier in encompass specific regions of
  • 06:22the prefrontal and parietal cortices.
  • 06:23When we looked closely at the neural signal,
  • 06:26we did see that trials with better
  • 06:28working memory performance as shown
  • 06:29on the X axis was associated with
  • 06:31greater neural signals.
  • 06:32This suggested that these regions are
  • 06:34key to linking the brain effects for the
  • 06:37observed improvement in working memory.
  • 06:39Finally,
  • 06:40we wanted to know what happens
  • 06:42when participants win,
  • 06:43lose or avoid losing money based on
  • 06:45their working memory performance
  • 06:46and what we saw suggested that the
  • 06:48impact of this was emotionally felt.
  • 06:50We saw that winning money more money
  • 06:52was associated with greater neural
  • 06:54signal in brain regions that process
  • 06:56pleasure such as the ventral striatum
  • 06:58or nucleus accumbens shown in green.
  • 07:00Avoiding losing money was also
  • 07:02associated with pleasure and here
  • 07:03greater neural signal was also seen in
  • 07:05the ventral striatum shown in purple.
  • 07:07So there was some overlap here.
  • 07:09However,
  • 07:10greater amounts of money lost
  • 07:11was associated with.
  • 07:12Greater neural signal in regions
  • 07:14that process pain and disappointment,
  • 07:16including the habenula periaqueductal
  • 07:17Gray in the insula, as shown in red.
  • 07:21Overall,
  • 07:22this suggested clear engagement of
  • 07:24participants in our task and that
  • 07:26completing a cognitive task that was
  • 07:29incentivized affected internal emotions.
  • 07:31So from this work we concluded that
  • 07:34motivation improves working memory by
  • 07:35shaping neural signals in the posterior
  • 07:37prefrontal and parietal cortices.
  • 07:39The amount of money won,
  • 07:41lost or avoided in lost was encoded by
  • 07:43brain regions that process feelings,
  • 07:45such as pleasure, pain,
  • 07:47and disappointment.
  • 07:48And our future directions will include
  • 07:50two related studies.
  • 07:51In the first will test these effects
  • 07:53in adolescents with depression
  • 07:54using a longitudinal study design,
  • 07:56and in the second will use a
  • 07:58large publicly available data set
  • 08:00to understand how cognitive and
  • 08:01motivational abilities in children
  • 08:03may affect developmental trajectories
  • 08:05in risk for psychiatric illness.
  • 08:07Thank you,
  • 08:08thank you for watching this talk
  • 08:10and thank you to all who helped
  • 08:12and supported this study,
  • 08:13especially the research participants
  • 08:14in Teacher Bitch Lab.
  • 08:16At the end, three division,
  • 08:17the Department of Psychiatry
  • 08:19and Yell Child Study Center.
  • 08:20Thank you.