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 infor￾mation integration. Specifically, Rsp is heavily inter￾connected with the HF and parahippocampal cortex, receiving nearly 40% of its extrinsic input from the me￾dial 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 me￾dial 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 recipro￾cal 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 lat￾eral extent includes STG (Vincent et al. 2007a). Com￾plicating the picture, IPL is greatly expanded in hu￾mans, 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 in￾crease (Van Essen & Dieker 2007). Thus, these lateral parietal and temporo-parietal areas, which are not as well characterized as PCC/Rsp, are extremely interest￾ing in light of their anatomic connections, involvement in the default network, and potential evolutionary ex￾pansion in humans. The connectional anatomy of area 7m in the pre￾cuneus 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. Ref￾erences to precuneus in the neuroimaging literature are often used loosely to label the general region that includes PCC area 29/30. Precuneus area 7m pre￾dominantly 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 re￾gions 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 some￾times 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 net￾work 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 ex￾plicitly 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, en￾compasses a set of areas that lie along the frontal mid￾line (Petrides & Pandya 1994, Ong ¨ ur¨ & Price 2000). Human MPFC is greatly expanded relative to the mon￾key (Ong ¨ ur¨ et al. 2003, FIG. 6). Two differences are no￾table. First, macaque area 32 is pushed ventrally and rostrally in humans to below the corpus callosum (la￾beled by Ong ¨ ur¨ et al. as area 32pl in the human based on Brodmann’s original labeling of this area in mon￾key as the “prelimbic area”). Human area 32ac cor￾responds to Brodmann’s dorsal “anterior cingulate” area. Second, human area 10 is quite large and fol￾lows 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 analy￾ses 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)