Editing Working memory (section)

=== Localization in the brain ===
Localization of brain functions in humans has become much easier with the advent of [[brain imaging]] methods ([[Positron emission tomography|PET]] and [[fMRI]]). This research has confirmed that areas in the PFC are involved in working memory functions. During the 1990s much debate had centered on the different functions of the ventrolateral (i.e.,&nbsp;lower areas) and the [[Dorsolateral prefrontal cortex|dorsolateral (higher) areas of the PFC]]. A human lesion study provides additional evidence for the role of the [[dorsolateral prefrontal cortex]] in working memory.<ref>{{cite journal | vauthors = Barbey AK, Koenigs M, Grafman J | title = Dorsolateral prefrontal contributions to human working memory | journal = Cortex; A Journal Devoted to the Study of the Nervous System and Behavior | volume = 49 | issue = 5 | pages = 1195–1205 | date = May 2013 | pmid = 22789779 | pmc = 3495093 | doi = 10.1016/j.cortex.2012.05.022 }}</ref> One view was that the dorsolateral areas are responsible for spatial working memory and the ventrolateral areas for non-spatial working memory. Another view proposed a functional distinction, arguing that ventrolateral areas are mostly involved in pure maintenance of information, whereas dorsolateral areas are more involved in tasks requiring some processing of the memorized material. The debate is not entirely resolved but most of the evidence supports the functional distinction.<ref>{{cite journal | vauthors = Owen AM | title = The functional organization of working memory processes within human lateral frontal cortex: the contribution of functional neuroimaging | journal = The European Journal of Neuroscience | volume = 9 | issue = 7 | pages = 1329–1339 | date = July 1997 | pmid = 9240390 | doi = 10.1111/j.1460-9568.1997.tb01487.x | s2cid = 2119538 }}</ref>

Brain imaging has revealed that working memory functions are not limited to the PFC. A review of numerous studies<ref>{{cite journal | vauthors = Smith EE, Jonides J | title = Storage and executive processes in the frontal lobes | journal = Science | volume = 283 | issue = 5408 | pages = 1657–1661 | date = March 1999 | pmid = 10073923 | doi = 10.1126/science.283.5408.1657 | bibcode = 1999Sci...283.1657. }}</ref> shows areas of activation during working memory tasks scattered over a large part of the cortex. There is a tendency for spatial tasks to recruit more right-hemisphere areas, and for verbal and object working memory to recruit more left-hemisphere areas. The activation during verbal working memory tasks can be broken down into one component reflecting maintenance, in the left posterior parietal cortex, and a component reflecting subvocal rehearsal, in the left frontal cortex (Broca's area, known to be involved in speech production).<ref>{{cite journal | vauthors = Smith EE, Jonides J, Marshuetz C, Koeppe RA | title = Components of verbal working memory: evidence from neuroimaging | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 95 | issue = 3 | pages = 876–882 | date = February 1998 | pmid = 9448254 | pmc = 33811 | doi = 10.1073/pnas.95.3.876 | doi-access = free | bibcode = 1998PNAS...95..876S }}</ref>

There is an emerging consensus that most working memory tasks recruit a network of PFC and parietal areas. A study has shown that during a working memory task the connectivity between these areas increases.<ref>{{cite journal | vauthors = Honey GD, Fu CH, Kim J, Brammer MJ, Croudace TJ, Suckling J, Pich EM, Williams SC, Bullmore ET | display-authors = 6 | title = Effects of verbal working memory load on corticocortical connectivity modeled by path analysis of functional magnetic resonance imaging data | journal = NeuroImage | volume = 17 | issue = 2 | pages = 573–582 | date = October 2002 | pmid = 12377135 | doi = 10.1016/S1053-8119(02)91193-6 }}</ref> Another study has demonstrated that these areas are necessary for working memory, and not simply activated accidentally during working memory tasks, by temporarily blocking them through [[transcranial magnetic stimulation]] (TMS), thereby producing an impairment in task performance.<ref>{{cite journal | vauthors = Mottaghy FM | title = Interfering with working memory in humans | journal = Neuroscience | volume = 139 | issue = 1 | pages = 85–90 | date = April 2006 | pmid = 16337091 | doi = 10.1016/j.neuroscience.2005.05.037 | s2cid = 20079590 }}</ref>

A current debate concerns the function of these brain areas. The PFC has been found to be active in a variety of tasks that require executive functions.<ref name="Kane MJ, Engle RW 2002 637–71" /> This has led some researchers to argue that the role of PFC in working memory is in controlling attention, selecting strategies, and manipulating information in working memory, but not in maintenance of information. The maintenance function is attributed to more posterior areas of the brain, including the parietal cortex.<ref>{{cite journal | vauthors = Curtis CE, D'Esposito M | title = Persistent activity in the prefrontal cortex during working memory | journal = Trends in Cognitive Sciences | volume = 7 | issue = 9 | pages = 415–423 | date = September 2003 | pmid = 12963473 | doi = 10.1016/S1364-6613(03)00197-9 | s2cid = 15763406 }}</ref><ref name="Postle">{{cite journal | vauthors = Postle BR | title = Working memory as an emergent property of the mind and brain | journal = Neuroscience | volume = 139 | issue = 1 | pages = 23–38 | date = April 2006 | pmid = 16324795 | pmc = 1428794 | doi = 10.1016/j.neuroscience.2005.06.005 }}</ref> Other authors interpret the activity in parietal cortex as reflecting [[executive functions]], because the same area is also activated in other tasks requiring attention but not memory.<ref>{{cite journal | vauthors = Collette F, Hogge M, Salmon E, Van der Linden M | title = Exploration of the neural substrates of executive functioning by functional neuroimaging | journal = Neuroscience | volume = 139 | issue = 1 | pages = 209–221 | date = April 2006 | pmid = 16324796 | doi = 10.1016/j.neuroscience.2005.05.035 | hdl-access = free | s2cid = 15473485 | hdl = 2268/5937 }}</ref> Evidence from decoding studying employing multi-voxel-pattern-analysis of fMRI data showed the content of visual working memory can be decoded from activity patterns in visual cortex, but not prefrontal cortex.<ref name=":5">{{cite journal | vauthors = Sreenivasan KK, Curtis CE, D'Esposito M | title = Revisiting the role of persistent neural activity during working memory | journal = Trends in Cognitive Sciences | volume = 18 | issue = 2 | pages = 82–89 | date = February 2014 | pmid = 24439529 | pmc = 3964018 | doi = 10.1016/j.tics.2013.12.001 }}</ref> This led to the suggestion that the maintenance function of visual working memory is performed by visual cortex while the role of the prefrontal cortex is in executive control over working memory<ref name=":5" /> though it has been pointed out that such comparisons do not take into account the base rate of decoding across different regions.<ref>{{cite journal | vauthors = Bhandari A, Gagne C, Badre D | title = Just above Chance: Is It Harder to Decode Information from Prefrontal Cortex Hemodynamic Activity Patterns? | journal = Journal of Cognitive Neuroscience | volume = 30 | issue = 10 | pages = 1473–1498 | date = October 2018 | pmid = 29877764 | doi = 10.1162/jocn_a_01291 | s2cid = 46954312 }}</ref>

A 2003 meta-analysis of 60 neuroimaging studies found left [[Frontal lobe|frontal]] cortex was involved in low-task demand verbal working memory and right [[Frontal lobe|frontal]] cortex for spatial working memory. Brodmann's areas (BAs) [[Brodmann area 6|6]], [[Brodmann area 8|8]], and [[Brodmann area 9|9]], in the [[Superior frontal gyrus|superior frontal cortex]] was involved when working memory must be continuously updated and when memory for temporal order had to be maintained. Right Brodmann [[Brodmann area 10|10]] and [[Brodmann area 47|47]] in the ventral frontal cortex were involved more frequently with demand for manipulation such as dual-task requirements or mental operations, and Brodmann 7 in the [[posterior parietal cortex]] was also involved in all types of executive function.<ref>{{cite journal | vauthors = Wager TD, Smith EE | title = Neuroimaging studies of working memory: a meta-analysis | journal = Cognitive, Affective & Behavioral Neuroscience | volume = 3 | issue = 4 | pages = 255–274 | date = December 2003 | pmid = 15040547 | doi = 10.3758/cabn.3.4.255 | doi-access = free }}</ref> Updating information in visual working memory is also influenced by the functional neural network connecting different brain regions.<ref name=":6">{{Cite journal |last=Velichkovsky |first=B. B. |last2=Kozlovskiy |first2=S. A. |last3=Buldakova |first3=N. S. |last4=Ushakov |first4=V. L. |last5=Kartashov |first5=S. I. |last6=Vartanov |first6=A. V. |date=2018-10-01 |title=The neurocognitive mechanisms of working memory updating |url=https://linkinghub.elsevier.com/retrieve/pii/S0167876018307931 |journal=International Journal of Psychophysiology |series= |volume=131 |pages=S171–S172 |doi=10.1016/j.ijpsycho.2018.07.452 |issn=0167-8760|url-access=subscription }}</ref> The [[Dorsolateral prefrontal cortex|dorsolateral PFC]] plays a crucial role in this process. In particular, the [[middle frontal gyrus]] may be involved in the maintenance, and the frontal operculum in the controlled processing of materials in working memory.<ref name=":6" /> Studies have also shown the role of attentional switching in working memory updating, mediated by the [[superior parietal lobule]].<ref name=":6" /> Working memory updating also involves a repetition mechanism mediated by the temporal cortex.<ref name=":6" /> And in addition, the process of working memory updating involves the sensory cortex to encode and store certain visual stimuli, such as geometric shapes ([[inferior occipital gyrus]]) and faces ([[fusiform gyrus]]).<ref name=":6" />

Working memory has been suggested to involve two processes with different neuroanatomical locations in the frontal and parietal lobes.<ref name="Bledowski">{{cite journal | vauthors = Bledowski C, Rahm B, Rowe JB | title = What 'works' in working memory? Separate systems for selection and updating of critical information | journal = The Journal of Neuroscience | volume = 29 | issue = 43 | pages = 13735–13741 | date = October 2009 | pmid = 19864586 | pmc = 2785708 | doi = 10.1523/JNEUROSCI.2547-09.2009 }}</ref> First, a selection operation that retrieves the most relevant item, and second an updating operation that changes the focus of attention made upon it. Updating the attentional focus has been found to involve the transient activation in the caudal [[superior frontal sulcus]] and [[posterior parietal cortex]], while increasing demands on selection selectively changes activation in the rostral superior frontal sulcus and posterior cingulate/[[precuneus]].<ref name="Bledowski" />

Articulating the differential function of brain regions involved in working memory is dependent on tasks able to distinguish these functions.<ref name="Coltheart-2006">{{cite journal | vauthors = Coltheart M | title = What has functional neuroimaging told us about the mind (so far)? | journal = Cortex; A Journal Devoted to the Study of the Nervous System and Behavior | volume = 42 | issue = 3 | pages = 323–331 | date = April 2006 | pmid = 16771037 | doi = 10.1016/S0010-9452(08)70358-7 | s2cid = 4485292 }}</ref> Most brain imaging studies of working memory have used recognition tasks such as delayed recognition of one or several stimuli, or the n-back task, in which each new stimulus in a long series must be compared to the one presented n steps back in the series. The advantage of recognition tasks is that they require minimal movement (just pressing one of two keys), making fixation of the head in the scanner easier. Experimental research and research on individual differences in working memory, however, has used largely recall tasks (e.g.,&nbsp;the [[reading span task]], see below). It is not clear to what degree recognition and recall tasks reflect the same processes and the same capacity limitations.

Brain imaging studies have been conducted with the reading span task or related tasks. Increased activation during these tasks was found in the PFC and, in several studies, also in the [[anterior cingulate cortex]] (ACC). People performing better on the task showed larger increase of activation in these areas, and their activation was correlated more over time, suggesting that their neural activity in these two areas was better coordinated, possibly due to stronger connectivity.<ref>{{cite journal | vauthors = Kondo H, Osaka N, Osaka M | title = Cooperation of the anterior cingulate cortex and dorsolateral prefrontal cortex for attention shifting | journal = NeuroImage | volume = 23 | issue = 2 | pages = 670–679 | date = October 2004 | pmid = 15488417 | doi = 10.1016/j.neuroimage.2004.06.014 | s2cid = 16979638 }}</ref><ref>{{cite journal | vauthors = Osaka N, Osaka M, Kondo H, Morishita M, Fukuyama H, Shibasaki H | title = The neural basis of executive function in working memory: an fMRI study based on individual differences | journal = NeuroImage | volume = 21 | issue = 2 | pages = 623–631 | date = February 2004 | pmid = 14980565 | doi = 10.1016/j.neuroimage.2003.09.069 | s2cid = 7195491 }}</ref>