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...; Mizuno et al., 2011; see Schipul, Keller, & Just,s2011 for a recent review). We propose that the lower synchronization arises due tosa reduction of the maximal rate of data transfer (or bandwidth) (=-=Shannon, 1949-=-)sbetween frontal and posterior cortical areas in autism. Decreased bandwidthsimpacts performance of the brain system when the inter-regional communicationsneeds are high.sTo describe the implications...

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...ative environment can becomesmore autonomous when inter-agent communication is impaired (Stone & Veloso,s1999), and communication networks can switch to an asynchronous mode whensbandwidth decreases (=-=Fall, 2003-=-). Analogously, the underconnectivity theory of autismspredicts that decreased cortical bandwidth could result in concomitant adaptations inscortical functioning, most probably increased posterior (in...

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...NDERCONNECTIVITY 49sRELATION TO OTHER THEORIES OF AUTISMsThis section compares underconnectivity theory with previous theoretical approaches tosautism, such as the theories of weak central coherence (=-=Frith, 1989-=-), impaired complexsinformation processing (Minshew et al., 1997), enhanced perceptual functionings(Mottron, Dawson, Soulieres, Hubert, & Burack, 2006), mindblindness (Baron-Cohen,s1995), impaired soc...

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...et al., 2001,sCourchesne, Redcay, & Kennedy, 2004; Waiter et al., 2005), although typicallysdeveloping individuals show a linear increase in white matter volume between thesages of four and 22 years (=-=Giedd et al., 1999-=-).sThe most prominent white matter tract in the cortex, the corpus callosum, also showssabnormalities in autism. The corpus callosum enables communication amongsfunctional systems in the two hemispher...

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...s (Keller and Just, 2009a).sThese converging findings suggest that reductions in communication and connectivitysamong cortical regions may be part of the pervasive core processing deficits in autisms(=-=Belmonte et al., 2004-=-; Courchesne & Pierce, 2005a, 2005b; Herbert et al., 2004; Just etsal., 2004; Keller et al., 2007; Rippon, Brock, Brown, & Boucher, 2007). Below, wesdescribe a theory of autism based on disruption of ...

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...evious theoretical approaches tosautism, such as the theories of weak central coherence (Frith, 1989), impaired complexsinformation processing (Minshew et al., 1997), enhanced perceptual functionings(=-=Mottron, Dawson, Soulieres, Hubert, & Burack, 2006-=-), mindblindness (Baron-Cohen,s1995), impaired social processing and motivation (Dawson et al., 2002), and longerdistance cortical communication. Each of these theories captures some fundamentalsaspec...

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..., Cherkassky,sKeller, & Minshew, 2004), and many studies have replicated these findings instasks that require synchronization between frontal and posterior regions of thesbrain (Damarla et al., 2010; =-=Just et al., 2004-=-; Just, Cherkassky, Keller, Kana, &sMinshew, 2007; Kana, Keller, Cherkassky, Minshew, & Just, 2006, 2009; Kana,sKeller, Minshew, & Just, 2007; Koshino et al., 2005, 2008; Mason, Williams,sKana, Minshe...

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...sThese theorists suggest that the enlargement of brain size in autism during the earlysstages of development, described above (Aylward, Minshew, Field, Sparks, & Singh,s2002; Courchesne et al., 2001; =-=Courchesne, Carper, & Akshoomoff, 2003-=-; Piven et al.,s1995; Sparks et al., 2002), increases the cortical distance between key processingscenters, resulting in disruption of distant inter-regional communication. Specifically,sthis hypothes...

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...9a).sThese converging findings suggest that reductions in communication and connectivitysamong cortical regions may be part of the pervasive core processing deficits in autisms(Belmonte et al., 2004; =-=Courchesne & Pierce, 2005-=-a, 2005b; Herbert et al., 2004; Just etsal., 2004; Keller et al., 2007; Rippon, Brock, Brown, & Boucher, 2007). Below, wesdescribe a theory of autism based on disruption of cortical connectivity.sUNDE...

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...ey brain areas involved in processing faces (the fusiform face area, or FFA)sdemonstrates hypoactivation with some displacement of location for people withsautism compared to controls (Schultz, 2005; =-=Schultz et al., 2000-=-). However, bysexpanding the focus to the cortical network involved in such tasks, the abnormalityscan be seen as a result of underconnectivity. In a study using the n-back workingsmemory task with fa...

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...e, one of theskey brain areas involved in processing faces (the fusiform face area, or FFA)sdemonstrates hypoactivation with some displacement of location for people withsautism compared to controls (=-=Schultz, 2005-=-; Schultz et al., 2000). However, bysexpanding the focus to the cortical network involved in such tasks, the abnormalityscan be seen as a result of underconnectivity. In a study using the n-back worki...

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...scents with autism foundsreduced fractional anisotropy in white matter adjacent to the ventromedial prefrontalscortices, anterior cingulate gyri, temporoparietal junction, and in the corpus callosums(=-=Barnea-Goraly et al., 2004-=-). Reduced fractional anisotropy persists into adulthood insthe corpus callosum and in tracts in the frontal and temporal lobes (Alexander et al.,s2007; Keller, Kana, & Just, 2007; Lee et al., 2007). ...

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...hat this deviation was greatest in the radiate whitesmatter in the frontal lobe (Herbert et al., 2004). Later in life, adolescents and adultsswith autism actually exhibit reduced white matter volume (=-=Courchesne et al., 2001-=-,sCourchesne, Redcay, & Kennedy, 2004; Waiter et al., 2005), although typicallysdeveloping individuals show a linear increase in white matter volume between thesages of four and 22 years (Giedd et al....

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... behavioral studies (notsnecessarily from the corresponding brain-imaging studies). For instance, poorerscomprehension of complex syntax in autism was observed in the Detroit Test ofsOral Directions (=-=Minshew, Goldstein, & Siegel, 1997-=-), and good performance atsword recognition was observed by Newman et al. (2007). In general, the tendencysis for the autism group to process tasks in a way that relies less on functions thatshave a v...

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...sindividuals with autism during Theory of Mind (ToM) processing are centrally causal tosthe disorder. Many behavioral and neuroimaging studies have demonstrated this deficits(e.g., Baron-Cohen, 1989; =-=Happe, 1995-=-; Tager-Flusberg, 1992; Castelli, Frith, Happe,s& Frith, 2002; Kana et al., 2009) and its biological substrates in the right posteriorssuperior temporal sulcus and the nearby temporo-parietal junction...

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...ons of thesbrain (Damarla et al., 2010; Just et al., 2004; Just, Cherkassky, Keller, Kana, &sMinshew, 2007; Kana, Keller, Cherkassky, Minshew, & Just, 2006, 2009; Kana,sKeller, Minshew, & Just, 2007; =-=Koshino et al., 2005-=-, 2008; Mason, Williams,sKana, Minshew, & Just, 2008; Mizuno et al., 2011; see Schipul, Keller, & Just,s2011 for a recent review). We propose that the lower synchronization arises due tosa reduction o...

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.... Poor synchronization of activation has been demonstrated in tasksssuch as language comprehension (Just et al., 2004; Kana et al., 2006; Mason et al.,s2008; Mizuno et al., 2011), executive function (=-=Just et al., 2007-=-), social processings(Kana et al., 2009; Koshino et al., 2008; Schipul, Williams, Keller, Minshew, & Just,s2012), working memory (Koshino et al., 2005, 2008), high-level inhibition (Kana et al.,s2007;...

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...ntiation, axon genesis, and plasticity (Coyle, Leski, & Morrison,s2002), and several authors have proposed that autism is related to glutamatergicsdysfunction (Carlsson, 1998; Polleux & Lauder, 2004; =-=Rubenstein & Merzenich, 2003-=-).sIrregularities in these two amino acids, and potentially others, could be a factor in thesabnormal development of connections and functioning in people with autism.sIn summary, the disruption of co...

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...ions, it is actuallysbiologically plausible. The frontal lobes are implicated in many of the developmentalsmechanisms that may be relevant to autism, including glial activation andsneuroinflammation (=-=Vargas et al., 2005-=-); minicolumnopathy (Casanova et al., 2006);sincrease in neuron number (Courchesne et al., 2011); and early brain overgrowths(Carper et al., 2002, Carper & Courchesne, 2005; Herbert et al., 2004). Giv...

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...INGsCONNECTIVITYsIrregularities in a number of early neurodevelopmental processes could individually orsin combination result in abnormalities in the brain's development of white mattersconnectivity (=-=Bailey et al., 1998-=-; Geschwind & Levitt, 2007). For instance,sspecialized glial cells, oligodendrocytes, are responsible for the production of myelin,swhich enhances neural transmission. Other glial cells manage waste a...

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...rtical regions may be part of the pervasive core processing deficits in autisms(Belmonte et al., 2004; Courchesne & Pierce, 2005a, 2005b; Herbert et al., 2004; Just etsal., 2004; Keller et al., 2007; =-=Rippon, Brock, Brown, & Boucher, 2007-=-). Below, wesdescribe a theory of autism based on disruption of cortical connectivity.sUNDERCONNECTIVITY THEORYsThe cortical underconnectivity theory (Just et al., 2004, 2007) posits that interregiona...

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...ated these findings instasks that require synchronization between frontal and posterior regions of thesbrain (Damarla et al., 2010; Just et al., 2004; Just, Cherkassky, Keller, Kana, &sMinshew, 2007; =-=Kana, Keller, Cherkassky, Minshew, & Just, 2006-=-, 2009; Kana,sKeller, Minshew, & Just, 2007; Koshino et al., 2005, 2008; Mason, Williams,sKana, Minshew, & Just, 2008; Mizuno et al., 2011; see Schipul, Keller, & Just,s2011 for a recent review). We p...

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...9a).sThese converging findings suggest that reductions in communication and connectivitysamong cortical regions may be part of the pervasive core processing deficits in autisms(Belmonte et al., 2004; =-=Courchesne & Pierce, 2005-=-a, 2005b; Herbert et al., 2004; Just etsal., 2004; Keller et al., 2007; Rippon, Brock, Brown, & Boucher, 2007). Below, wesdescribe a theory of autism based on disruption of cortical connectivity.sUNDE...

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...el is expressed withinsthe 4CAPS cognitive neuroarchitecture, which accounts for cortical function in terms ofsa set of collaborating computational centers intended to correspond to cortical centerss(=-=Just & Varma, 2007-=-). The autism model of the Tower of London task is an adaptationsof a previous TOL model developed to account for the brain activation and performancesof typically developing individuals (Newman, Carp...

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...in autism during the earlysstages of development, described above (Aylward, Minshew, Field, Sparks, & Singh,s2002; Courchesne et al., 2001; Courchesne, Carper, & Akshoomoff, 2003; Piven et al.,s1995; =-=Sparks et al., 2002-=-), increases the cortical distance between key processingscenters, resulting in disruption of distant inter-regional communication. Specifically,sthis hypothesis predicts that individuals with autism ...

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...nctional connectivity betweensfrontal and posterior areas of the default network (regions more active during rest thansthey are during an externally imposed task) is lower in autism than in controlss(=-=Cherkassky, Kana, Keller, & Just, 2006-=-). This reduction in functional connectivityspersists even when high-frequency fluctuations in activation are filtered out (in anseffort to limit measurement to spontaneous physiological changes rathe...

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...ssan underlying mechanism that relates the biological and psychological levels.sTHEORY OF CORTICAL UNDERCOMMECTIVITY 51sAutism as a Complex Information Processing DisordersMinshew and her colleagues (=-=Minshew & Goldstein, 1998-=-; Minshew et al., 1997;sWilliams, Goldstein, & Minshew, 2006) have observed impairment in autism acrosssmany domains when the complexity level of information processing is high. Lowerlevel processes a...

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...her areas.sThe increased brain size observed in children with autism is largely due to volumesdifferences in white matter, particularly in the frontal lobes (Carper, Moses, Tigue, &sCourchesne, 2002, =-=Herbert et al., 2004-=-). One study reported overall greater whitesmatter volume in 7- to 11-year-old children with autism (Herbert et al., 2003), and thesauthors found in a later study that this deviation was greatest in t...

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...ronalsmigration, differentiation, axon genesis, and plasticity (Coyle, Leski, & Morrison,s2002), and several authors have proposed that autism is related to glutamatergicsdysfunction (Carlsson, 1998; =-=Polleux & Lauder, 2004-=-; Rubenstein & Merzenich, 2003).sIrregularities in these two amino acids, and potentially others, could be a factor in thesabnormal development of connections and functioning in people with autism.sIn...

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...even when high-frequency fluctuations in activation are filtered out (in anseffort to limit measurement to spontaneous physiological changes rather thanscognitively driven modulations of activation) (=-=Assaf et al., 2010-=-; Kennedy &sCourchesne, 2008; Monk et al., 2009; Weng et al., 2010). This finding has beensreplicated with EEG methods, measuring activity across cortical areas within the alphasrange (8-10 Hz) (Coben...

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...eatest in the radiate whitesmatter in the frontal lobe (Herbert et al., 2004). Later in life, adolescents and adultsswith autism actually exhibit reduced white matter volume (Courchesne et al., 2001,s=-=Courchesne, Redcay, & Kennedy, 2004-=-; Waiter et al., 2005), although typicallysdeveloping individuals show a linear increase in white matter volume between thesages of four and 22 years (Giedd et al., 1999).sThe most prominent white mat...

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...tion between a frontalslanguage area and a parietal spatial processing area (Kana et al., 2006). Yet another wassa task requiring complex inhibition, displaying reduced frontal-parietal connectivitys(=-=Kana et al., 2007-=-). Finally, even in a resting state when participants were notsperforming any assigned task, the functional underconnectivity in autism betweensfrontal and posterior regions continued to be manifested...

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... Varma, 2007). The autism model of the Tower of London task is an adaptationsof a previous TOL model developed to account for the brain activation and performancesof typically developing individuals (=-=Newman, Carpenter, Varma, & Just, 2003-=-). (Thestask required re-arranging the positions of three distinctive balls in three suspended poolspockets until they matched a specified goal [or ending] configuration, as shown insFigure 3.4.) The ...

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...pus callosum, also showssabnormalities in autism. The corpus callosum enables communication amongsfunctional systems in the two hemispheres. It is usually slightly smaller in individualsswith autism (=-=Chung, Dalton, Alexander, & Davidson, 2004-=-; Hardan, Minshew, &sKeshavan, 2000; Manes et al., 1999; Piven, Bailey, Ranson, & Arndt, 1997; Vidal etsal., 2006). As noted above, total brain size is abnormal in autism, and larger brainsvolume is c...

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...s been demonstrated in tasksssuch as language comprehension (Just et al., 2004; Kana et al., 2006; Mason et al.,s2008; Mizuno et al., 2011), executive function (Just et al., 2007), social processings(=-=Kana et al., 2009-=-; Koshino et al., 2008; Schipul, Williams, Keller, Minshew, & Just,s2012), working memory (Koshino et al., 2005, 2008), high-level inhibition (Kana et al.,s2007; Solomon et al., 2009), and visuospatia...

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... 2010; Kennedy &sCourchesne, 2008; Monk et al., 2009; Weng et al., 2010). This finding has beensreplicated with EEG methods, measuring activity across cortical areas within the alphasrange (8-10 Hz) (=-=Coben, Clarke, Hudspeth, & Barry, 2008-=-; Murias, Webb, Greenson,s& Dawson, 2007). Coben et al. (2008) interpreted their EEG results as indicating "...sdysfunctional integration of frontal and posterior brain regions in autistics along with...

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...hesformation of insulating white matter around axons.sTHEORY OF CORTICAL UNDERCONMECTIVITY 37sThe myelin sheath can increase the transmission speed and bandwidth of an axon by asfactor of 10 or more (=-=Hartline & Colman, 2007-=-), so myelination and its distributionshave a clear relation to cortical communication capacities, including synchronization.sIn addition, several studies have reported white matter volumetric abnorma...

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...ion are filtered out (in anseffort to limit measurement to spontaneous physiological changes rather thanscognitively driven modulations of activation) (Assaf et al., 2010; Kennedy &sCourchesne, 2008; =-=Monk et al., 2009-=-; Weng et al., 2010). This finding has beensreplicated with EEG methods, measuring activity across cortical areas within the alphasrange (8-10 Hz) (Coben, Clarke, Hudspeth, & Barry, 2008; Murias, Webb...

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...ated and incompletelysor aberrantly formed minicolumn vertical circuitry. Abnormalsminicolumn organization can result in an imbalance between excitation and inhibitionswithin and between minicolumns (=-=Courchesne, Redcay, Morgan, & Kennedy, 2005-=-), orsan abundance of short connective fibers relative to long ones, which may lead to asdeficiency in inter-regional connectivity. More numerous and abnormally narrowsminicolumns in frontal and tempo...

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..., social processings(Kana et al., 2009; Koshino et al., 2008; Schipul, Williams, Keller, Minshew, & Just,s2012), working memory (Koshino et al., 2005, 2008), high-level inhibition (Kana et al.,s2007; =-=Solomon et al., 2009-=-), and visuospatial processing (Damarla et al., 2010). Theslower synchronization, or functional connectivity, in autism measured during tasksperformance reflects the lower degree of coordination betwe...

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...may reveal possible branching points in development of differentssyndromes.sAnother disorder that involves disruption of white matter, like autism andsdevelopmental language delay, is dyslexia (e.g., =-=Deutsch et al., 2005-=-). Recently, wesdemonstrated that the white matter abnormalities associated with poor reading skills inschildren can be improved with training (Keller & Just, 2009b). If white matter issmodifiable wit...

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... the frontal lobe (Herbert et al., 2004). Later in life, adolescents and adultsswith autism actually exhibit reduced white matter volume (Courchesne et al., 2001,sCourchesne, Redcay, & Kennedy, 2004; =-=Waiter et al., 2005-=-), although typicallysdeveloping individuals show a linear increase in white matter volume between thesages of four and 22 years (Giedd et al., 1999).sThe most prominent white matter tract in the cort...

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...t (in anseffort to limit measurement to spontaneous physiological changes rather thanscognitively driven modulations of activation) (Assaf et al., 2010; Kennedy &sCourchesne, 2008; Monk et al., 2009; =-=Weng et al., 2010-=-). This finding has beensreplicated with EEG methods, measuring activity across cortical areas within the alphasrange (8-10 Hz) (Coben, Clarke, Hudspeth, & Barry, 2008; Murias, Webb, Greenson,s& Dawso...

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...rectionality of white matter fibers. At very young ages (two orsthree years), there is evidence of increased fractional anisotropy in autism, particularly insthe frontal lobe and corpus callosum (Ben =-=Bashat et al., 2007-=-), consistent with earlysovergrowth of white matter, discussed above. By five years of age, however, fractionalsanisotropy is reduced for tracts that connect regions within the frontal lobes (Sundaram...

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...ommunication amongsfunctional systems in the two hemispheres. It is usually slightly smaller in individualsswith autism (Chung, Dalton, Alexander, & Davidson, 2004; Hardan, Minshew, &sKeshavan, 2000; =-=Manes et al., 1999-=-; Piven, Bailey, Ranson, & Arndt, 1997; Vidal etsal., 2006). As noted above, total brain size is abnormal in autism, and larger brainsvolume is correlated with smaller corpus callosum size (Jancke, Pr...

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...shown evidence of both reduced (Jones etsal., 2010; Villalobos, Mizuno, Dahl, Kemmotsu, & Muller, 2005) and increaseds(Mizuno, Villalobos, Davies, Dahl, & Muller, 2006; Noonan, Haist, & Muller, 2009;s=-=Turner, Frost, Linsenbardt, Mcllroy, & Muller, 2006-=-; Shih et al., 2010) task-freesfunctional connectivity in autism relative to controls. Although the significance ofsthese results remains unclear, both increases and decreases in task-free functionals...

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...Goraly et al., 2004). Reduced fractional anisotropy persists into adulthood insthe corpus callosum and in tracts in the frontal and temporal lobes (Alexander et al.,s2007; Keller, Kana, & Just, 2007; =-=Lee et al., 2007-=-). Cumulatively, these studies providesclear evidence of a relationship between autism and disruption of the white matter thatsprovides the anatomical connectivity among frontal and posterior brain re...

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....sAlterations in white matter can impair thought processes. White matter propertiessare key determinants of the conduction velocity and hence the bandwidth of thescommunication channels in the brain (=-=Waxman, 1980-=-), thereby impacting corticalsconnectivity. One such property is the degree of myelination of axons, or thesformation of insulating white matter around axons.sTHEORY OF CORTICAL UNDERCONMECTIVITY 37sT...

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...particularly apparent in autism.sLong-Distance ConnectivitysSome researchers have suggested that long-range, but not short-range, brainsconnectivity may be disrupted in autism (Belmonte et al., 2004; =-=Lewis & Elman, 2008-=-).sThese theorists suggest that the enlargement of brain size in autism during the earlysstages of development, described above (Aylward, Minshew, Field, Sparks, & Singh,s2002; Courchesne et al., 2001...

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...ch assfaces.sAnother proposed explanation for impaired social processing in autism centers aroundsatypical development of the ability to initiate joint attention (IJA) (Mundy, Sigman, &sKasari, 1994; =-=Mundy, Sullivan, & Mastergeorge, 2009-=-). This theory suggests thatssocial referencing and learning depends on the initiation of joint attention, whichsrequires close collaboration between temporo-parietal and frontal areas. This proposals...

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...activation andsneuroinflammation (Vargas et al., 2005); minicolumnopathy (Casanova et al., 2006);sincrease in neuron number (Courchesne et al., 2011); and early brain overgrowths(Carper et al., 2002, =-=Carper & Courchesne, 2005-=-; Herbert et al., 2004). Given thesprotracted maturation of frontal lobe circuitry, these abnormalities could affect onlysfrontal-posterior tracts, resulting in underconnectivity specifically along wh...

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...bandwidth couldsgive rise to increased functional connectivity among posterior regions.sCOMPUTATIONAL MODELING OF BRAIN FUNCTIONsAND COGNITIONsHere we briefly describe a recent computational account (=-=Just et al., 2012-=-) of the lowersfrontal-posterior functional connectivity and longer response times in autism in a highlevel visual problem-solving task, the Tower of London. The model is expressed withinsthe 4CAPS co...

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...ate, affects neuronalsmigration, differentiation, axon genesis, and plasticity (Coyle, Leski, & Morrison,s2002), and several authors have proposed that autism is related to glutamatergicsdysfunction (=-=Carlsson, 1998-=-; Polleux & Lauder, 2004; Rubenstein & Merzenich, 2003).sIrregularities in these two amino acids, and potentially others, could be a factor in thesabnormal development of connections and functioning i...

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...e ofsthese results remains unclear, both increases and decreases in task-free functionalsconnectivity could plausibly reduce the available bandwidth of communication forstask-relevant processing (see =-=Schipul et al., 2011-=-, for a discussion).sSimilarly, underconnectivity is evident during a resting state in which the "task"sconsists of relaxed, internally generated thought. The functional connectivity betweensfrontal a...

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...mprehension task (Just, Cherkassky,sKeller, & Minshew, 2004), and many studies have replicated these findings instasks that require synchronization between frontal and posterior regions of thesbrain (=-=Damarla et al., 2010-=-; Just et al., 2004; Just, Cherkassky, Keller, Kana, &sMinshew, 2007; Kana, Keller, Cherkassky, Minshew, & Just, 2006, 2009; Kana,sKeller, Minshew, & Just, 2007; Koshino et al., 2005, 2008; Mason, Wil...

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..., 2003), have been demonstrated in several brainsregions in autism, including cingulate gyrus, temporal gray matter, frontal and parietalswhite matter, hippocampal-amygdaloid complex, and cerebellum (=-=Friedman et al., 2003-=-;sHisaoka, Harada, Nishitani, & Mori, 2001; Levitt et al., 2003; Otsuka, Harada, Mori,sHisaoka, & Nishitani, 1999). Another amino acid, glutamate, affects neuronalsmigration, differentiation, axon gen...

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...CONNECTIVITY 43sautism-related differences in hemispheric lateralization of fractional anisotropy in thesarcuate fasciculus connecting frontal, parietal, and temporal cortices (Fletcher et al.,s2010; =-=Knaus et al., 2010-=-). One study of children and adolescents with autism foundsreduced fractional anisotropy in white matter adjacent to the ventromedial prefrontalscortices, anterior cingulate gyri, temporoparietal junc...

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...illalobos, Mizuno, Dahl, Kemmotsu, & Muller, 2005) and increaseds(Mizuno, Villalobos, Davies, Dahl, & Muller, 2006; Noonan, Haist, & Muller, 2009;sTurner, Frost, Linsenbardt, Mcllroy, & Muller, 2006; =-=Shih et al., 2010-=-) task-freesfunctional connectivity in autism relative to controls. Although the significance ofsthese results remains unclear, both increases and decreases in task-free functionalsconnectivity could ...

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... processing (Minshew et al., 1997), enhanced perceptual functionings(Mottron, Dawson, Soulieres, Hubert, & Burack, 2006), mindblindness (Baron-Cohen,s1995), impaired social processing and motivation (=-=Dawson et al., 2002-=-), and longerdistance cortical communication. Each of these theories captures some fundamentalsaspect of autism, and all of them are at least partially correct. However, many of thesespredecessor theo...

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..., particularly in the frontal lobes (Carper, Moses, Tigue, &sCourchesne, 2002, Herbert et al., 2004). One study reported overall greater whitesmatter volume in 7- to 11-year-old children with autism (=-=Herbert et al., 2003-=-), and thesauthors found in a later study that this deviation was greatest in the radiate whitesmatter in the frontal lobe (Herbert et al., 2004). Later in life, adolescents and adultsswith autism act...

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...y, Keller, Kana, &sMinshew, 2007; Kana, Keller, Cherkassky, Minshew, & Just, 2006, 2009; Kana,sKeller, Minshew, & Just, 2007; Koshino et al., 2005, 2008; Mason, Williams,sKana, Minshew, & Just, 2008; =-=Mizuno et al., 2011-=-; see Schipul, Keller, & Just,s2011 for a recent review). We propose that the lower synchronization arises due tosa reduction of the maximal rate of data transfer (or bandwidth) (Shannon, 1949)sbetwee...

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...nstrated in several brainsregions in autism, including cingulate gyrus, temporal gray matter, frontal and parietalswhite matter, hippocampal-amygdaloid complex, and cerebellum (Friedman et al., 2003;s=-=Hisaoka, Harada, Nishitani, & Mori, 2001-=-; Levitt et al., 2003; Otsuka, Harada, Mori,sHisaoka, & Nishitani, 1999). Another amino acid, glutamate, affects neuronalsmigration, differentiation, axon genesis, and plasticity (Coyle, Leski, & Morr...

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... (connectingsthe frontal and temporal lobes) or the left inferior frontal-occipital fasciculus, observedsin a sample of 52 adults and adolescents with autism compared to age- and IQ-matchedscontrols (=-=Keller and Just, 2009-=-a).sThese converging findings suggest that reductions in communication and connectivitysamong cortical regions may be part of the pervasive core processing deficits in autisms(Belmonte et al., 2004; C...

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...As discussed above, fMRI studies havesdemonstrated that synchronization between frontal and posterior areas is lower insautism (Just et al., 2004, 2007; Kana et al., 2006, 2007; Koshino et al., 2005;s=-=Villalobos et al., 2005-=-). Figure 3.2A (see plate section) illustrates this deficit insconnectivity when participants complete a Tower of London (TOL) problem-solvingstask, which entails activation of both frontal and pariet...

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...he deficits seen insindividuals with autism during Theory of Mind (ToM) processing are centrally causal tosthe disorder. Many behavioral and neuroimaging studies have demonstrated this deficits(e.g., =-=Baron-Cohen, 1989-=-; Happe, 1995; Tager-Flusberg, 1992; Castelli, Frith, Happe,s& Frith, 2002; Kana et al., 2009) and its biological substrates in the right posteriorssuperior temporal sulcus and the nearby temporo-pari...

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...svolume is correlated with smaller corpus callosum size (Jancke, Preis, & Steinmetz,s1999; Jancke, Staiger, Schlaug, Huang, & Steinmetz, 1997), suggesting multiple locisof disruption in connectivity (=-=Ringo, 1991-=-). The abnormalities in white matter insautism, including myelination and corpus callosum size, form a plausible neural basissfor disrupted systems-level connectivity in autism.sBIOLOGICAL MECHANISMS ...