《认知神经科学》课程教学资源（参考文献）[Buckner, R. L., Andrews-Hanna, J. R., & Schacter, D. L.（2008）]The brain's default network - Anatomy, function, and relevance to disease.pdf_P6-P10

Buckner eta:The Brain's Default Network Event-Related,Task-Induced Deactivation An alternative to defining the anatomy of the de- 0m2005.D2 Vincent et al.2006).Functional con it ana related (MRI make is particularly informative because it provides a means senting task trials at randomly jittered time int to assess locations of interacting brain regions within typically 2 to 10seconds apart.The reason to perform the default network in a manner that is independent such an analysis is the possibility that extended epochs of task-induced deactivation.In their initial studics are required to clicit activity during passive cpochs,as Greicius ct al.measured spontancous activityom th might be the case ifblocked task a core reg the de from sl cd ta a rapi :(c.g. ogether.Their map of the default network.based on FICURE 3 illustrates the results of a metacanalsis of intrinsic functional correlations,is remarkably similar tudies from Shannon(2006)that uses event-related to that originally generated by Shulman ct al.(1997) MRI data to define the default network.In total,data based on PET vations. from 49 subjects were pooled for this analysis. The mpor from anal 0 c and p og Kirchho in the emn yolved scmantic classification (Shannon 2006:n=21). are associated with episodic mem- ory function (Greicius et al.2004).In fact,many of As can be anpreciated visually the default network de the major neocortical regi ons constituting the default fined based on event-related data is higbly similar to network can be revealed by placing a seed region in that previously reported using blocked data.I hus,the the hippocampal formation and mapping thos c cort differential activity in the default network between pas- rstates can ntancous on( cmerge rapidly,on the ed fron tions with the hipp ampal formation in four inde- Functional Connectivity Analysis pendent data sets. A final approach to defining the functional anatomy of the default network is based on the measurement of Convergence across Approache the brain's intrinsic Def ining the Default Networ Is th en the of the de brain systems (Biswal ct al.1995,De Luc a1.2006 ork desc there exists spontancous activity that tracks the func ribed abo dan amd tional and anatomic organization of the brain.The fault network anatomy is displayed on the bottom panel patterns of spontaneous activity are believed to re- of FIGURE3.The convergence reveals that the default network comprises a distributed set of regions that et al onal contributions ncludes ex an sory and ex(PCC/Rsp),and the inferior arictal lobule IPL) orain with fRI and can he used to characterize the intrinsic architecture of large-scale brain systems, an approach often referred to as functional connec Several more specifc observations are apparent tivity MRI(Biswal et al.1995,Haughton Biswal from this analysis of overlap.First,the hippocampal a.1995200 nation (HF)issho wn t H al 2006) pproach the de aL2006 ns have been characterizcd usine func nalysis)but.relative to the robust tional connectivity analysis(see also De Luca et al. 2006). nent using the approach of task-induced deactivations

Buckner et al.: The Brain’s Default Network 7 Event-Related, Task-Induced Deactivation An alternative to defining the anatomy of the default network based on blocked tasks is to perform a similar analysis on individual task events. Rapid eventrelated fMRI makes possible such an analysis by presenting task trials at randomly jittered time intervals, typically 2 to 10 seconds apart. The reason to perform such an analysis is the possibility that extended epochs are required to elicit activity during passive epochs, as might be the case if blocked task-induced deactivations arise from slowly evolving signals or sustained task sets that are not modulated on a rapid time frame (e.g., Dosenbach et al. 2006). FIGURE 3 illustrates the results of a meta-analysis of studies from Shannon (2006) that uses event-related fMRI data to define the default network. In total, data from 49 subjects were pooled for this analysis. The data are based on semantic and phonological classifi- cation tasks from Kirchhoff et al. (2005; n = 28) as well as a second sample of event-related data that also involved semantic classification (Shannon 2006; n = 21). As can be appreciated visually, the default network de- fined based on event-related data is highly similar to that previously reported using blocked data. Thus, the differential activity in the default network between passive and active task states can emerge rapidly, on the order of seconds or less. Functional Connectivity Analysis A final approach to defining the functional anatomy of the default network is based on the measurement of the brain’s intrinsic activity. At all levels of the nervous system from individual neurons (Tsodyks et al. 1999) and cortical columns (Arieli et al. 1995) towholebrain systems (Biswal et al. 1995, De Luca et al. 2006), there exists spontaneous activity that tracks the functional and anatomic organization of the brain. The patterns of spontaneous activity are believed to re- flect direct and indirect anatomic connectivity (Vincent et al. 2007a) although additional contributions may arise from spontaneous cognitive processes (as will be described in a latersection). In humans, low-frequency, spontaneous correlations are detectable across the brain with fMRI and can be used to characterize the intrinsic architecture of large-scale brain systems, an approach often referred to as functional connectivity MRI (Biswal et al. 1995, Haughton & Biswal 1998; see Fox & Raichle 2007 for a recent review). Motor (Biswal et al. 1995), visual (Nir et al. 2006), auditory (Hunter et al. 2006), and attention (Fox et al. 2006) systems have been characterized using functional connectivity analysis (see also De Luca et al. 2006). Greicius and colleagues (2003, 2004) used such an analysisto map the brain’s default network (see also Fox et al. 2005, Fransson 2005, Damoiseaux et al. 2006, Vincent et al. 2006). Functional connectivity analysis is particularly informative because it provides a means to assess locations of interacting brain regions within the default network in a manner that is independent of task-induced deactivation. In their initial studies, Greicius et al. measured spontaneous activity from the posterior cingulate cortex, a core region in the default network, and showed that activity levels in the remaining distributed regions of the system are all correlated together. Their map of the default network, based on intrinsic functional correlations, is remarkably similar to that originally generated by Shulman et al. (1997) based on PET deactivations. An important further observation from analyses of intrinsic activity is that the default network includes the hippocampus and adjacent areas in the medial temporal lobe that are associated with episodic memory function (Greicius et al. 2004). In fact, many of the major neocortical regions constituting the default network can be revealed by placing a seed region in the hippocampal formation and mapping those cortical regions that show spontaneous correlation (Vincent et al. 2006). FIGURE 3 shows a map of the default network as generated from intrinsic functional correlations with the hippocampal formation in four independent data sets. Convergence across Approaches for Defining the Default Network Is there convergence between the three distinct approaches for defining the anatomy of the default network described above? To answer this question, the overlap among the multiple methods for defining default network anatomy is displayed on the bottom panel of FIGURE 3. The convergence reveals that the default network comprises a distributed set of regions that includes association cortex and spares sensory and motor cortex. In particular, medial prefrontal cortex (MPFC), posterior cingulate cortex/retrosplenial cortex (PCC/Rsp), and the inferior parietal lobule (IPL) show nearly complete convergence across the 18 data sets. Several more specific observations are apparent from this analysis of overlap. First, the hippocampal formation (HF) is shown to be involved in the default network regardless of which approach is used (task-induced deactivation or functional connectivity analysis) but, relative to the robust posterior midline and prefrontal regions, the HF is less prominent using the approach of task-induced deactivations

8 Annals of the New York Academy of Sciences FIGURE 4. The default network in the monkey defined using functional connectivity analysis. A seed was placed in the posterior midline (indicated by asterisk) and the regions showing correlated activity were mapped. The left image shows the medial surface, the middle image a transverse section through parietal cortex, and the right image a coronal section through the hippocampal formation. Left is plotted on the left. Adapted from Vincent et al. (2007a). Second, multiple default network regions are functionally correlated with the HF, reinforcing the notion that the medial temporal lobe is included in the network. Overlap is not perfect, however, with some indications of more extensive recruitment during passive cognitive states, including both in posterior parietal cortex and in prefrontal cortex. These details will be shown to be informative when subsystems within the default network are discussed. Third, lateral temporal cortex (LTC) extending into the temporal pole is consistently observed across approaches but, like the HF, is less robust. Together these observations tentatively define the core anatomical components of the default network (TABLE 1). Insights from Comparative Anatomy Important insights into the organization of human brain systems have been provided by comparative studies in the monkey. Vincent et al. (2007a) recently used functional connectivity analysis to show that the major default network regions in posterior cortex have putative monkey homologues including PCC/Rsp, IPL, and the HF (FIG. 4, see also Rilling et al. 2007). In addition, architectonic maps reveal many similarities between human and monkey anatomy in the vicinity of the default network (e.g., Petrides & Pandya 1994, Morris et al. 2000, Ong ¨ ur¨ & Price 2000, Vogt et al. 2001). Motivated by these recent observations, we provide here a detailed analysis of the architectonics and connectional anatomy of the default network, while recognizing that there may be fundamental differences in humans. As a means to simplify our analysis, we focus on areas that fall within PCC/Rsp and MPFC and their anatomic relationships with other cortical regions and the HF. Potentially important subcortical connections, such as to the striatal reward pathway and the amygdala, are not covered. Even with this simplification, the details of the anatomy are complex and one is immediately confronted with the observation that each of the activated regions, as defined based on human functional neuroimaging data, extends across multiple brain areas that have distinct architecture and connectivity. Progress will require significantly more detailed analysis of the anatomic extent and locations of default network regions in humans. Nonetheless, using available data we provide an initial analysis of the anatomy recognizing that it is provisional and incomplete. Posterior cingulate cortex (PCC) and restrosplenial cortex (Rsp) have been extensively studied in the macaque monkey and recently so with focus on direct comparison to human anatomy (e.g., Morris et al. 2000, Vogt et al. 2001). The PCC and Rsp fall along the posterior midline and exist within a region that contains at least three contiguous, but distinct, sets of areas: Rsp (areas 29/30), PCC (areas 23/31), and precuneus (area 7m). Rsp is just posterior to the corpus callosum and, in humans, extends along the ventral bank of the cingulate gyrus (Morris et al. 2000, Vogt et al. 2001). In macaques, Rsp is much smaller and does not encroach onto the cingulate gyrus (Morris et al. 1999, Kobayashi & Amaral 2000). Just posterior to Rsp, along the main portion of the cingulate gyrus, is PCC. The precuneus, a region often cited as being involved in the default network, comprises the posterior and dorsal portion of the medial parietal lobe and includes area 7m (Cavanna & Trimble 2006, Parvizi et al. 2006). As an ensemble, these three structures are sometimes referred to as “posteriomedial

Buckner et al.:The Brain's Default Network 9 not a componen The predominant extrinsic conn ections to and from the posteriomedial cortex difter by area collectively includes PCC area 29/30.Precuncus area 7m pre the connections are widespread and,much like other dominantly connects with occipital and parietal areas association areas,are con stent with a role in infor- mation integration.Specifically,Rsp is heavily inter- oacR and par Leichnetz 2001).Moreover,medial tem poral lobe 12003 show na m.C Cand Rsp ashi&An Amrl 1004 Morris et al 1900) ca 7m and the PCC.which ma omoiects back to the medial temporal lobe as well as be the basis for the extensive activation patterns som prominently to multiple prefrontal regions(Kobayashi times observed along the posterior midline,but we Amaral 2007,FIG.5).PCC area 23 has reciprocal suspect that area 7m is not a core component of the e and robust forcing thisi se exam ion of 1 he the hur uman IPL (Koba maps tha Amaral 2003.2007.FIG.5).The medial te ent of the network usually does not encroach on the also has modest but consistent connections with arca dge of the parietal midline(where arca 7m is located 7a(Suzuki Amaral 1994,Cloweretal.2001,Lavenex Scheperjans et al.2007).This boundary is labeled ex et al.2002).Thus,PCC/Rsp provides a key hub for plicitly in FIGURE7 by an asterisk.The middlle panel tween the c mc of FiGURE 18 shows a particularly clear obe,an n the An unresoledissue is whether the lateral ectiot netuork and a zone of PCC/Rsp is restricted to area 7a in humans (2004;their Figure 2A versus 2B).For all these reasons, or extends to areas 39/40.Macaque PCC has recipro we provisionally conclude that area 7m in precuneus cal projections to superior temporal sulcus(STS)and is not part of the default network The second of th MPF areas t 1004 STG Vincent etal.2007a).Com 200 Huma plicating the picture.IPL is g atly expanded in hu ey (Onguir et al.2003,FIG.6).Two differences are no mans,including areas 39/40(Culham Kanwisher table.First.macaque area 32 is pushed ventrally and 2001,Simon et al.2002,Orban et al.2006)that are rostrally in humans to below the corpus callosum (a- closely localized to the lateral parietal regior beled ct al.as area 3pln the human based ing on Br ion be the brain based on ma ows the rostral path of anterior cingulate areas 24 crease(Van Essen Dieker 2007).Thus,these lateral and 32ac much like typical activation of MPFC in the default network.This is relevant because commonly referenced maps based on classic architectonic analy and pote n in h natel The conn ctional anat r of area 7m in the pre to cialization default network even though it is often included in 2001)

Buckner et al.: The Brain’s Default Network 9 cortex,” and each structure is interconnected with the others (e.g., Parvizi et al. 2006, Kobayashi & Amaral 2003). The predominant extrinsic connections to and from the posteriomedial cortex differ by area. Collectively, the connections are widespread and, much like other association areas, are consistent with a role in information integration. Specifically, Rsp is heavily interconnected with the HF and parahippocampal cortex, receiving nearly 40% of its extrinsic input from the medial temporal lobe (Kobayashi & Amaral 2003, see also Suzuki & Amaral 1994, Morris et al. 1999). Rsp also projects back to the medial temporal lobe as well as prominently to multiple prefrontal regions (Kobayashi & Amaral 2007, FIG. 5). PCC area 23 has reciprocal connections with the medial temporal lobe and robust connections with prefrontal cortex and parietal cortex area 7a—an area at or near the putative homologue of the human default network region IPL (Kobayashi & Amaral 2003, 2007, FIG. 5). The medial temporal lobe also has modest, but consistent, connections with area 7a (Suzuki&Amaral 1994, Clower et al. 2001, Lavenex et al. 2002). Thus, PCC/Rsp provides a key hub for overlapping connections between themselves, the medial temporal lobe, and IPL—three of the distributed regions that constitute the major posterior extent of the default network. An unresolved issue is whether the lateral projection zone of PCC/Rsp is restricted to area 7a in humans or extends to areas 39/40. Macaque PCC has reciprocal projections to superior temporal sulcus (STS) and the superior temporal gyrus (STG; see also Kobayashi & Amaral 2003). Analysis of the default network in macaques provides indication that the network’s lateral extent includes STG (Vincent et al. 2007a). Complicating the picture, IPL is greatly expanded in humans, including areas 39/40 (Culham & Kanwisher 2001, Simon et al. 2002, Orban et al. 2006) that are closely localized to the lateral parietal region identified by human neuroimaging as being within the default network (see Caspers et al. 2006). A recent analysis of cortical expansion between the macaque and human brain based on mapping of 23 presumed homologies revealed that IPL is among the regions of greatest increase (Van Essen & Dieker 2007). Thus, these lateral parietal and temporo-parietal areas, which are not as well characterized as PCC/Rsp, are extremely interesting in light of their anatomic connections, involvement in the default network, and potential evolutionary expansion in humans. The connectional anatomy of area 7m in the precuneus is difficult to understand in relation to the default network even though it is often included in the default network. One possibility is that area 7m is simply not a component of the default network. References to precuneus in the neuroimaging literature are often used loosely to label the general region that includes PCC area 29/30. Precuneus area 7m predominantly connects with occipital and parietal areas linked to visual processing and frontal areas associated with motor planning (Cavada& Goldman-Rakic 1989, Leichnetz 2001). Moreover, medial temporal lobe regions that have extensive projections to PCC and Rsp show minimal connections to area 7m. Connections do exist between area 7m and the PCC, which may be the basis for the extensive activation patterns sometimes observed along the posterior midline, but we suspect that area 7m is not a core component of the network. Reinforcing this impression, close examination of the many maps that define the human default network in this review shows that the posterior medial extent of the network usually does not encroach on the edge of the parietal midline (where area 7m is located, Scheperjans et al. 2007). This boundary is labeled explicitly in FIGURE 7 by an asterisk. The middle panel of FIGURE 18 shows a particularly clear example of the separation between task-induced deactivation of PCC and its dissociation from the region at or near area 7m. Another example of dissociation between the default network and area 7m can be found in Vogeley et al. (2004; their Figure 2A versus 2B). For all these reasons, we provisionally conclude that area 7m in precuneus is not part of the default network. The second hub of the default network, MPFC, encompasses a set of areas that lie along the frontal midline (Petrides & Pandya 1994, Ong ¨ ur¨ & Price 2000). Human MPFC is greatly expanded relative to the monkey (Ong ¨ ur¨ et al. 2003, FIG. 6). Two differences are notable. First, macaque area 32 is pushed ventrally and rostrally in humans to below the corpus callosum (labeled by Ong ¨ ur¨ et al. as area 32pl in the human based on Brodmann’s original labeling of this area in monkey as the “prelimbic area”). Human area 32ac corresponds to Brodmann’s dorsal “anterior cingulate” area. Second, human area 10 is quite large and follows the rostral path of anterior cingulate areas 24 and 32ac much like typical activation of MPFC in the default network. This is relevant because commonly referenced maps based on classic architectonic analyses restrict this area to frontalpolar cortex (e.g., Petrides & Pandya 1994). Some evidence suggests that area 10 is disproportionately expanded in humans even when contrasted to great apes, suggesting specialization during recent hominid evolution (Semendeferi et al. 2001)