It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. Joe Hardy reports on a study by Backman et al in Science, where from the authors report:. Updating of working memory has been associated with striato-frontal brain regions and phasic dopaminergic neurotransmission.
We assessed raclopride binding to striatal dopamine DA D2 receptors during a letter-updating task and a control condition before and after 5 weeks of updating training. Results showed that updating affected DA activity before training and that training further increased striatal DA release during updating. These findings highlight the pivotal role of transient neural processes associated with D2 receptor activity in working memory. This result shows that cognitive training with exercises similar to those on Lumosity can change the way the brain works at a fundamental chemical level.
The paper claims that training on updating based on the influential view of executive function proposed by Miyake et al. Hardy is therefore stretching the study conclusions quite far here. As Tyler Langan notes in his comment to the question, the effect of a neurotransmitter is enormously dependent on a number of factors beyond the type of transmitter, such as exactly where it is released, and for how long it is released, among others.
In some sufficiently broad sense, it is probably true that "cognitive training leads to enhanced dopamine release," but I don't necessarily think that is meaningful in any explanatory sense. When interpreting fMRI studies, it is always important to consider very, very carefully the exact relationship between the evidence and the claim, especially when venturing beyond the careful boundaries set down by the original authors.
Consider, for instance, the carefully bounded conclusion reached by the original authors:. Our data are consistent with findings of displacement of ligand binding to D2 receptors during cognitive processing 5, 8 and indicate a link between previously observed increases of BOLD activity after WM training 1 and DA release. To the best of our knowledge, this is the first demonstration of changes in neurotransmission in relation to transfer of learning.
For n-back the peak response was in right striatum, whereas the corresponding effect for letter memory was in left striatum. The reason for the difference in laterality remains unclear, and was not expected from our previous observation of a training-related overlap in left caudate BOLD signal change for letter memory and n-back 1.
In agreement with several recent meta-analyses and qualitative reviews 8 , 9 , 10 , 11 , we found no evidence that updating training transferred to performance on the tasks included in the off-line battery tapping verbal and spatial working memory, motor speed, episodic memory, set shifting, and inhibitory control. Moreover, unlike the findings reported by Dahlin et al. The reason thereof may be that the present participants performed at a very high level for 3-back already at the pre-training assessment.
The high level may reflect the length more room for task practice and the nature of the task performed during scanning, which likely increases the perceived performance demands compared to an off-line testing situation.
Note also that recent meta-analyses indicate that effect sizes for this form of near-transfer are quite small 9 , 10 , Thus, it is unsurprising that such transfer effects may or may not be observed in a specific study. This is especially true in PET research with relatively small sample sizes and limited statistical power. In view of this concern and even though the measurement scale might not have been sensitive enough to capture behavioral transfer effects, the PET data nevertheless demonstrated DA alterations during the untrained n-back task.
The present pattern of results raises the possibility that increased DA release may be a necessary, but not sufficient, condition for behavioral transfer to occur.
The present research extends previous observations that the DA system is plastic. Such plasticity has been observed during both pharmacological and cognitive challenges 18 , 20 , 21 , 27 , 28 , 29 , 30 , The current replication of increased striatal DA release during letter memory after WM updating training, and the novel result of a corresponding increase during an untrained 3-back task, provide additional evidence that the DA system is malleable.
The effective sample included 28 right-handed healthy, non-smoking, and non-medicated Finnish male university students 19—26 years. The participants underwent structural MRI and medical screening.
The study was approved by the Ethics Review Board of the Turku University Hospital District, the methods were carried out in accordance with relevant guidelines and regulations, and written informed consent was obtained from all participants.
We employed a pre-training—intervention—post-training control group design. All participants took part in the pre- and post-training assessments, whereas only participants in the training group received training between these assessments. The pre-training assessments included a structural MRI scan, neuropsychological testing, and two consecutive PET scans performed during the same day.
Time in-between the pre- and post-training assessments was 6—9 weeks. The training program was a computerized in-house developed Visual Basic program and consisted of the letter memory criterion task and five other updating tasks 1 , Four of the additional training tasks were similar to the letter memory task and involved updating of single items, but to foster generality different kinds of stimuli i.
In these training tasks, five lists of items were randomly presented and the task was to recall the four last presented items. All subjects reached the most difficult level by the end of training.
The final training task was a keep-track task. This task, too, taxes updating, but is structurally different from the other updating tasks in the training battery.
The inclusion of the keep-track task should contribute toward strengthening of a general updating skill. In each trial, 15 words from different semantic categories were presented serially in random order 2.
They had to continuously update their working memory content and remember the last presented word in each category at the end of the presentation. Participants responded by typing the last presented word under each category box when the trial ended. The pre- and post-training PET scans were identical: both involved two scans of which one was performed in the morning and the other in the afternoon. The letter-memory task was administered during the morning scan, whereas the digit n-back task was administered during the afternoon scan.
The two assessments were separated by a min lunch break. During the first PET scan, we administered a computerized letter-memory task that taps verbal WM updating. Participants were shown 7—15 letters in a sequence; when a sequence suddenly ended, they were asked to report the last four letters in correct order by pressing buttons corresponding to A, B, C, and D. This task was preceded by a structurally equivalent control task not taxing updating all letters in a sequence were identical and participants reported that letter.
Prior to PET scanning, participants acquainted themselves with the task during a practice session. The sequence began with instructions shown for ms. Stimulus duration was ms with a fixation cross in-between for ms. The participants were allowed ms to respond. During the second PET scan, the participants performed a digit n-back task that measures verbal WM updating. In this task, they were to determine if a currently visible digit was the same as the previous digit 1-back or the digit that was presented three steps back 3-back.
The dependent measure was target accuracy on the 3-back vs. After participants had read the task instructions and completed one 1-back and one 3-back practice task, the PET session was initiated. Task instructions, informing the participant of which n-back version to perform, were shown at the beginning of each task version for ms, after which a digit was shown for ms.
The digit was replaced by a fixation point that was visible for ms, and after this the fixation point was once again replaced by a digit. The alternation of fixation points and digits continued until the end of the task.
The participants responded by pressing a match button for targets and a non-match button for non-targets. The only differences between the studies concerned the duration of the letter- memory and digit n-back tasks performed during the PET scans.
In other respects, the letter-memory tasks were identical. Raclopride was prepared from [ 11 C]methyl triflate following an established procedure At scan start, the actual bolus injection and infused doses did not differ between groups or scans Table 3. Before each emission scan, a transmission scan was performed using a Cs point source. Tissue-attenuation maps were reconstructed using the maximum a posteriori transmission data MAP-TR algorithm with segmentation.
Scattered events were estimated using the single-scatter simulation algorithm, and randoms were estimated from the block singles with a variance-reduction algorithm. All corrections were applied within the statistical image-reconstruction algorithm Special attention was paid to minimization of head-motion artifacts based on earlier observations of its detrimental effects on the PET signal and its interpretation Specifically, head motion was minimized using an individually molded thermoplastic mask, and image reconstructions were made using an in-house version of the multiple-acquisition frame MAF 36 based motion-compensated image reconstruction algorithm.
The algorithm employs external motion tracking MT as given by Vicra Northern Digital infrared detection, to define motion-free amplitude less than 2. This procedure compensates for attenuation map misalignments using mutual information- based image registration and finally combines the motion-free subframes into original, desired framing. In a phantom study by Johansson et al. Rapidly oscillating, high amplitude motion is not often observed in human PET scans but, if present, may introduce erroneous perturbations in the PET signal, which in turn could be incorrectly interpreted as activation effects 36 , On the basis of visual inspection of the motion data, five letter-memory scans from four individuals, and three n-back scans from two individuals were deemed unrecoverable using the motion-compensation algorithm, and were thus excluded from analysis.
In addition to those excluded due to extensive motion, the letter-memory PET variables of four subjects were missing due to other technical reasons. Thus, a total of eight participants were missing from the PET letter-memory analysis, resulting in an n of In turn, the n-back PET variables were missing from three subjects, two of whom were not scanned after training, and in one case the data acquisition failed. Hence, altogether five participants were missing from the n-back analysis, resulting in an n of Structural MR imaging was performed for excluding anatomical abnormalities and for anatomical reference of the PET data.
The PET-image analysis was restricted to striatum, which serves as a central hub of dopaminergic activation. Extensive spatial smoothing was deemed necessary for successful calculation of binding potential BP from the PET activation data.
Modeling of the dynamic PET data was based on an extension of the conventional simplified reference tissue model SRTM 40 , including the effect of activation as an additional parameter. A similar approach as described by Alpert and colleagues 41 was adopted, where the activation effect on the 11 C-raclopride signal was modeled by the time-dependent activation function h t , and the relevant linear equations are:.
Compared to our previous work 19 , we now employed an explicit BP calculation algorithm for the activation phase, to quantitatively assess the magnitude of this effect relative to baseline. Model calculation was restricted to the aforementioned striatal volume, and the resulting parametric images were normalized using the MRI-based deformation into MNI space coordinates.
Variance smoothing was used with an FWHM of 10 mm. The pre- and post-training neuropsychological assessments included three WAIS-III subtests digit span, letter-number sequencing, and digit symbol , a number-letter task, a Simon task, a visuospatial n-back task, and an episodic recall task.
The digit span test was used to assess auditory attention as well as passive forward span and active backward span WM. Participants were asked to recall sequences of digits in the same or reversed order in which they were presented.
Maximum forward and backward spans were used as dependent measures. Several lines of research indicate that dopamine plays an important role not only in WM function but also for improving WM capacity. For example, pharmacological interventions acting on the dopaminergic system, such as methylphenidate, improve WM performance. The training programme can be found on-line, see link further down.
Compared to a control group that did not receive any training, the trained group showed a gradual improvement of working-memory performance. Results from a PET scan demonstrated an increased release of dopamine in the caudate after training.
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