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when asked to give an account of his creative process , albert einstein reported that language played virtually no role in his thought process .  the psychical entities which seem to serve as elements in thought
when einstein s brain was examined postmortem , it was noted that among other irregularities , the inferior parietal lobe was significantly larger than normal .
the posterior parietal cortex ( ppc ) plays a central role in multisensory integration   and environmental - spatial cognition .
many recent human imaging ( and also some monkey neurophysiology ) studies demonstrate that the ppc additionally supports various forms of high - order non - spatial cognition that are not necessarily directly related to physical space itself .
for example , while the superior parietal lobule ( spl ) tends to process spatial information in a conventional way , the inferior parietal lobule ( ipl ) is often credited with non - spatial cognition .
the ipl is said to be evolutionarily new and uniquely expanded in humans and the monkey ppc is said to correspond to the human spl , but there is another view that the monkey ppc possesses functional homologues of both regions .
if the latter view is correct , neuroscientists should be able to identify precursory mechanisms of non - spatial information processing in non - human primates .
indeed , when monkeys were trained to acquire tool use - a high - order behavior they rarely exhibit naturally - ppc expansion was observed at both microscopic   and macroscopic   scales .
( a ) monkey ppc ; ( b ) human left ppc ; ( c ) human right ppc
. results of meta - analysis ( based on the references listed in figure 2 ) of cortical areas responsible for non - spatial cognition are superimposed .
data points in monkeys are projected onto the left hemisphere ( because no particular laterality has been claimed ) , whereas those in human subjects are illustrated independently for each hemisphere ( being biased toward the left hemisphere ) .
large and dashed symbols indicate areas estimated from reviews and original papers , respectively , in which coordinates were not clearly specified .
arabic numerals indicate brodmann areas ( 40 : supramarginal gyrus ; 39 : angular gyrus ) .
aip , anterior intraparietal area ; cip , caudal intraparietal area ; cs , central sulcus ; ips , intraparietal sulcus ; lip , lateral intraparietal area ; mip , medial intraparietal area ; pcs , post central sulcus ; pos , parieto - occipital sulcus ; sf , sylvian fissure ; sts , superior temporal sulcus ; vip , ventral intraparietal area .
the following section reviews various recently reported forms of non - spatial representation in the ppc . they are ordered roughly in terms of the level of abstraction of the  objects and pseudo - spatial relations represented ( figure 2 ) .
the last section considers potential mechanisms that could have enabled the hominid ppc to establish such representations and hypothesizes a general principle to unify these newer forms of representation with the ppc s original functions .
left , hypothesized mechanism for increasing abstract levels of representations ( see  future directions section for details ) .
right , structure of various levels of abstract spaces ( references for respective levels are listed in the far - right column ) .
3d , three - dimensional ; 4d , four - dimensional ; ag , angular gyrus ; aip , anterior intraparietal area ; cip , caudal intraparietal area ; ipl , inferior parietal lobule ; ips , intraparietal sulcus ; lip , lateral intraparietal area ; ppc , posterior parietal cortex ; sii , secondary somatosensory cortex ; smg , supramarginal gyrus ; spl , superior parietal lobule ; tpj , temporo - parietal junction .
the ppc is implicated in three - dimensional ( 3d ) object recognition , processing of number and quantity , attention , and memory .
the intraparietal sulcus ( ips ) and anterior intraparietal area are activated when concrete 3d objects are recognized , explored , imagined , and constructed .
discerning continuous quantity recruits the anterior ips   while discrete number processing recruits the bilateral ips [ 14 - 16 ] , forming a mental number line   and mental arithmetic . sustained attention to spatial locations recruits the area between the right ips and the ipl .
the lateral intraparietal area responds to various features of the stimulus shape [ 20 - 25 ] .
angular gyrus and temporo - parietal junction ( tpj ) activity is related to stimulus saliency detection and control .
the left and right posterior tpj are active while processing global and local information , respectively .
the ppc may play a critical role in working memory [ 30 - 33 ] , although this region can also be active during tasks requiring no working memory .
thus , the ppc s apparent role in working memory may reflect a broader function , such as temporally transferring information from present to future ( see  temporal space section ) .
the tpj plays a crucial role in temporal order judgment tasks   as well as in magnitude judgments about numbers .
the ppc supports time interval estimation and is active when estimating future object position . in the ppc
the ppc processes some aspects of social space , including action understanding , tool use , and self - other relationships , thereby enabling imitation .
the ppc is one of the brain areas showing mirror properties [ 42 - 44 ] .
imitation activates the left inferior parietal cortex more than observation does , regardless of first- or third - person perspective .
the human anterior ips distinguishes between observed and executed movements , suggesting that ppc neurons have hierarchical properties for recognizing sameness or difference of kinematics , goals , and function of motion .
the ppc supports tool usage , an extension of the bodily self [ 49 - 52 ] .
this faculty may require an implicit equivalence to be drawn between innate body parts and external objects . a proposed brain network subserving such body - part objectification includes the ppc .
evaluations of physical and social distance to others involve the superior and inferior ppc , respectively , in accordance with egocentric distance estimation by the parietal cortex .
cooperative and competitive tasks recruit a common set of brain regions with competition activating the right inferior parietal lobe more strongly , reflecting the apparent contrast between self and others .
the ppc s facility with both concrete spatial cognition and self - other discrimination may have preadapted it to handle perspective transformation in social situations .
this in turn could have laid the basis for further functional expansion into realms such as social categorization and , later in evolution , conceptual spaces .
finally , the ppc appears to play a role in causal reasoning , mental object manipulation , attention switching , set shifting , and dimensional abstraction .
in addition to the role of the ppc in tool usage ( see  social space section ) , different ppc areas support broad concepts such as the causal ramifications of using tools   and the logical structures of the gestures involved .
the spl and smg are differentially activated during rotations of visual and motor imagery , respectively .
spatial scanning through mental imagery activated the precuneus , spl , ipl , and ips .
the ppc is responsible for mentally manipulating sequentially learned materials , whereas the mid - dorsolateral prefrontal cortex is responsible for monitoring the learned items .
ppc activation is also related to cognitive set shifting [ 65 - 70 ] . during a visual search with attention shifts ,
ppc activation was diminished in elderly people in the solution - search phase of a set - shifting task .
perspective taking   is one of the prominent qualitative distinctions between the attention - shifting abilities of humans and other primates .
ppc activity also correlates with abstract information at various levels and dimensions [ 74 - 77 ] and with modulation of the strength of the visual stimulus and motor planning .
the left parietal cortex is involved in the cortical rearranging of the relationship between semantic items in space .
the ppc is implicated in three - dimensional ( 3d ) object recognition , processing of number and quantity , attention , and memory .
the intraparietal sulcus ( ips ) and anterior intraparietal area are activated when concrete 3d objects are recognized , explored , imagined , and constructed .
discerning continuous quantity recruits the anterior ips   while discrete number processing recruits the bilateral ips [ 14 - 16 ] , forming a mental number line   and mental arithmetic . sustained attention to spatial locations recruits the area between the right ips and the ipl .
the lateral intraparietal area responds to various features of the stimulus shape [ 20 - 25 ] .
angular gyrus and temporo - parietal junction ( tpj ) activity is related to stimulus saliency detection and control .
the left and right posterior tpj are active while processing global and local information , respectively .
the ppc may play a critical role in working memory [ 30 - 33 ] , although this region can also be active during tasks requiring no working memory .
thus , the ppc s apparent role in working memory may reflect a broader function , such as temporally transferring information from present to future ( see  temporal space section ) .
the tpj plays a crucial role in temporal order judgment tasks   as well as in magnitude judgments about numbers .
the ppc supports time interval estimation and is active when estimating future object position . in the ppc ,
the ppc processes some aspects of social space , including action understanding , tool use , and self - other relationships , thereby enabling imitation .
the ppc is one of the brain areas showing mirror properties [ 42 - 44 ] .
imitation activates the left inferior parietal cortex more than observation does , regardless of first- or third - person perspective .
the human anterior ips distinguishes between observed and executed movements , suggesting that ppc neurons have hierarchical properties for recognizing sameness or difference of kinematics , goals , and function of motion .
the ppc supports tool usage , an extension of the bodily self [ 49 - 52 ] .
this faculty may require an implicit equivalence to be drawn between innate body parts and external objects .
evaluations of physical and social distance to others involve the superior and inferior ppc , respectively , in accordance with egocentric distance estimation by the parietal cortex .
cooperative and competitive tasks recruit a common set of brain regions with competition activating the right inferior parietal lobe more strongly , reflecting the apparent contrast between self and others .
the ppc s facility with both concrete spatial cognition and self - other discrimination may have preadapted it to handle perspective transformation in social situations .
this in turn could have laid the basis for further functional expansion into realms such as social categorization and , later in evolution , conceptual spaces .
finally , the ppc appears to play a role in causal reasoning , mental object manipulation , attention switching , set shifting , and dimensional abstraction .
in addition to the role of the ppc in tool usage ( see  social space section ) , different ppc areas support broad concepts such as the causal ramifications of using tools   and the logical structures of the gestures involved .
the spl and smg are differentially activated during rotations of visual and motor imagery , respectively .
spatial scanning through mental imagery activated the precuneus , spl , ipl , and ips .
the ppc is responsible for mentally manipulating sequentially learned materials , whereas the mid - dorsolateral prefrontal cortex is responsible for monitoring the learned items .
ppc activation is also related to cognitive set shifting [ 65 - 70 ] . during a visual search with attention shifts ,
ppc activation was diminished in elderly people in the solution - search phase of a set - shifting task .
perspective taking   is one of the prominent qualitative distinctions between the attention - shifting abilities of humans and other primates .
ppc activity also correlates with abstract information at various levels and dimensions [ 74 - 77 ] and with modulation of the strength of the visual stimulus and motor planning .
the left parietal cortex is involved in the cortical rearranging of the relationship between semantic items in space .
as outlined above and illustrated in figure 2 ( right ) , various kinds of non - spatial cognition can be grouped and ordered based on the levels of abstraction of the  objects and ideally defined spaces represented . assumed coordinate systems for such 
the pseudo - spatial nature of the high - order cognition supported by the ppc may derive from the essential characteristics of the objects represented but alternatively may derive from the nature of the ppc s pre - existing information - processing mechanisms , namely as a hub for multisensory integration and representing physical environmental space .
the meta - analysis in figure 1 illustrates that the ppc areas responsible for these novel forms of cognition are not necessarily clearly segregated , either in monkeys or humans , but does suggest a trend of gradual expansion toward the ipl as the level of abstraction proceeds .
thus , it seems that the ppc gradually incorporated high - order cognition as it expanded during hominid evolution while preserving its original principles of operation .
what is the explanation for this expansion of function ? here is a hypothesis involving mechanisms for  selecting and  switching between objects among different represented spaces : ( a ) in classical ( physical ) space , spatial attention toward concrete objects was typically expressed as eye movement ; ( b ) when such attention needed to be sustained or when the attending content needed to be memorized , invisible 
visualized in the mind s eye , becoming a new virtual dimension in the ppc s existing suite of spatial coordinate systems ; ( c ) once the ppc could visualize an invisible virtual entity , a similar objectification process could be extended further , enabling intentional perspective switching ( figure 2 , left ) .
acquiring representations of social space might have accelerated this process . through objectification processes   and the development of  virtual eyes , flexible and mutually integrated representations of the bodily self ,
the analogous selves of others , and tools as equivalents of body parts ( and vice versa ) might have served as a bridge between concrete physical and abstract conceptual spaces . as the ppc expanded in both physical volume and range of function   ( figure 2 , dashed circle ) , a positive feedback process ( arrow ) could have been established to achieve further human - specific forms of non - spatial conceptual cognition .
thus , crucial components of human intelligence derive their character from the precursorial spatial cognition process of the ppc . indeed , language is rife with spatial metaphors for abstract thoughts .
non - human primates possess the same precursorial parietal mechanisms as human ancestors ; through training , their cognitive capacities can be artificially extended in the hominid / human direction . if correct , this hypothesis will be valuable in guiding the design of future experimental paradigms , in both animal and human studies , to elucidate the principles of parietal information processing .
the primate posterior parietal cortex ( ppc ) processes information related to environmental physical space . 
 the human ppc has apparently expanded not only in size but also in its functional range to encompass certain abstract and higher - order conceptual spaces . in this report 
 , we review various forms of non - spatial representation in the ppc . 
 these forms are presented roughly in order of the level of abstraction of the  objects and pseudo - spatial relations represented . also , we consider mechanisms that could have enabled the hominid ppc to establish such representations . 
 lastly , we offer a general principle to unify the newer forms of representation with the original functions of the ppc .