Editing Broca's area (section)

==Functions==

===Language comprehension===

For a long time, it was assumed that the role of Broca's area was more devoted to language production than language comprehension. However, there is evidence to demonstrate that Broca's area also plays a significant role in language comprehension. Patients with [[lesions]] in Broca's area who exhibit agrammatical speech production also show inability to use syntactic information to determine the meaning of sentences.<ref name="pmid16881251">{{cite journal | vauthors = Caplan D | title = Why is Broca's area involved in syntax? | journal = Cortex; A Journal Devoted to the Study of the Nervous System and Behavior | volume = 42 | issue = 4 | pages = 469–71 | date = May 2006 | pmid = 16881251 | doi = 10.1016/S0010-9452(08)70379-4 | s2cid = 4480694 }}</ref> Also, a number of neuroimaging studies have implicated an involvement of Broca's area, particularly of the [[pars opercularis]] of the left inferior frontal [[gyrus]], during the processing of complex sentences.<ref name="pmid15929098">{{cite journal | vauthors = Grewe T, Bornkessel I, Zysset S, Wiese R, von Cramon DY, Schlesewsky M | title = The emergence of the unmarked: a new perspective on the language-specific function of Broca's area | journal = Human Brain Mapping | volume = 26 | issue = 3 | pages = 178–90 | date = November 2005 | pmid = 15929098 | doi = 10.1002/hbm.20154 | url = http://edoc.mpg.de/244878 | pmc = 6871720 }}</ref> Further, [[functional magnetic resonance imaging]] (fMRI) experiments have shown that highly ambiguous sentences result in a more activated inferior frontal [[gyrus]].<ref name="pmid15635062">{{cite journal | vauthors = Rodd JM, Davis MH, Johnsrude IS | title = The neural mechanisms of speech comprehension: fMRI studies of semantic ambiguity | journal = Cerebral Cortex | volume = 15 | issue = 8 | pages = 1261–9 | date = August 2005 | pmid = 15635062 | doi = 10.1093/cercor/bhi009 | doi-access = free }}</ref> Therefore, the activity level in the inferior frontal gyrus and the level of lexical ambiguity are directly proportional to each other, because of the increased retrieval demands associated with highly ambiguous content.

There is also specialisation for particular aspects of comprehension within Broca's area. Work by Devlin et al. (2003)<ref>{{cite journal | vauthors = Devlin JT, Matthews PM, Rushworth MF | title = Semantic processing in the left inferior prefrontal cortex: a combined functional magnetic resonance imaging and transcranial magnetic stimulation study | journal = Journal of Cognitive Neuroscience | volume = 15 | issue = 1 | pages = 71–84 | date = January 2003 | pmid = 12590844 | doi = 10.1162/089892903321107837 | citeseerx = 10.1.1.329.8485 | s2cid = 7570128 }}</ref> showed in a repetitive transcranial magnetic stimulation ([[Transcranial magnetic stimulation|rTMS]]) study that there was an increase in reaction times when performing a [[Semantics|semantic]] task under rTMS aimed at the [[pars triangularis]] (situated in the anterior part of Broca's area). The increase in reaction times is indicative that that particular area is responsible for processing that cognitive function. Disrupting these areas via TMS disrupts computations performed in the areas leading to an increase in time needed to perform the computations (reflected in reaction times). Later work by Nixon et al. (2004)<ref name=pmid15068598>{{cite journal | vauthors = Nixon P, Lazarova J, Hodinott-Hill I, Gough P, Passingham R | title = The inferior frontal gyrus and phonological processing: an investigation using rTMS | journal = Journal of Cognitive Neuroscience | volume = 16 | issue = 2 | pages = 289–300 | date = March 2004 | pmid = 15068598 | doi = 10.1162/089892904322984571 | s2cid = 1162060 | url = http://eprints.maynoothuniversity.ie/4866/1/PG_rTMS.pdf }}</ref> showed that when the pars opercularis (situated in the posterior part of Broca's area) was stimulated under rTMS there was an increase in reaction times in a [[Phonology|phonological]] task. Gough et al. (2005)<ref name=pmid16135758>{{cite journal | vauthors = Gough PM, Nobre AC, Devlin JT | title = Dissociating linguistic processes in the left inferior frontal cortex with transcranial magnetic stimulation | journal = The Journal of Neuroscience | volume = 25 | issue = 35 | pages = 8010–6 | date = August 2005 | pmid = 16135758 | pmc = 1403818 | doi = 10.1523/JNEUROSCI.2307-05.2005 }}</ref> performed an experiment combining elements of these previous works in which both phonological and semantic tasks were performed with rTMS stimulation directed at either the anterior or the posterior part of Broca's area. The results from this experiment conclusively distinguished anatomical specialisation within Broca's area for different components of language comprehension. Here the results showed that under rTMS stimulation: 
* [[Semantics|Semantic]] tasks only showed a decrease in reaction times when stimulation was aimed at the anterior part of Broca's area (where a decrease of 10% (50&nbsp;ms) was seen compared to a no-TMS control group)
* [[Phonological]] tasks showed a decrease in reaction times when stimulation was aimed at the posterior part of Broca's area (where a decrease of 6% (30&nbsp;ms) was seen compared to control)
To summarise, the work above shows anatomical specialisation in Broca's area for language comprehension, with the anterior part of Broca's area responsible for understanding the meaning of words (semantics) and the posterior part of Broca's area responsible for understanding how words sound (phonology).

===Action recognition and production===

Experiments have indicated that Broca's area is involved in various cognitive and perceptual tasks. One important contribution of [[Korbinian Brodmann|Brodmann]]'s area 44 is also found in the motor-related processes. Observation of meaningful hand shadows resembling moving animals activates frontal language area, demonstrating that Broca's area indeed plays a role in interpreting action of others.<ref name="pmid18633777">{{cite journal | vauthors = Fadiga L, Craighero L, Destro MF, Finos L, Cotillon-Williams N, Smith AT, Castiello U | title = Language in shadow | journal = Social Neuroscience | volume = 1 | issue = 2 | pages = 77–89 | year = 2006 | pmid = 18633777 | doi = 10.1080/17470910600976430 | s2cid = 20322 }}</ref> An activation of BA 44 was also reported during execution of grasping and manipulation.<ref name="pmid16881255">{{cite journal | vauthors = Fadiga L, Craighero L | title = Hand actions and speech representation in Broca's area | journal = Cortex; A Journal Devoted to the Study of the Nervous System and Behavior | volume = 42 | issue = 4 | pages = 486–90 | date = May 2006 | pmid = 16881255 | doi = 10.1016/S0010-9452(08)70383-6 | s2cid = 2463077 }}</ref>

===Speech-associated gestures===
It has been speculated that because speech-associated gestures could possibly reduce lexical or sentential ambiguity, comprehension should improve in the presence of speech-associated gestures. As a result of improved comprehension, the involvement of Broca's area should be reduced.<ref name="pmid17533001" />

Many neuroimaging studies have also shown activation of Broca's area when representing meaningful arm gestures. A recent study has shown evidence that word and gesture are related at the level of translation of particular gesture aspects such as its [[motor goal]] and intention.<ref name="pmid16839281">{{cite journal | vauthors = Gentilucci M, Bernardis P, Crisi G, Dalla Volta R | title = Repetitive transcranial magnetic stimulation of Broca's area affects verbal responses to gesture observation | journal = Journal of Cognitive Neuroscience | volume = 18 | issue = 7 | pages = 1059–74 | date = July 2006 | pmid = 16839281 | doi = 10.1162/jocn.2006.18.7.1059 | s2cid = 18159912 }}</ref> This finding helps explain why, when this area is defective, those who use sign language also have language deficits.<ref name=Carlson>{{cite book |last1=Carlson |first1=N. |year=2013 |chapter=Human Communication |title=Physiology of Behavior |edition=11th |location=Boston |publisher=Allyn and Bacon }}</ref>{{rp|494–7}} This finding, that aspects of gestures are translated in words within Broca's area, also explains language development in terms of evolution. Indeed, many authors have proposed that speech evolved from a primitive communication that arose from gestures.<ref name="pmid18633777"/><ref name="pmid12653308">{{cite journal | vauthors = Lieberman P | title = On the nature and evolution of the neural bases of human language | journal = American Journal of Physical Anthropology | volume = Suppl 35 | pages = 36–62 | year = 2002 | pmid = 12653308 | doi = 10.1002/ajpa.10171 | doi-access = free }}</ref> (See below.)

===Speaking without Broca's area===

Damage to Broca's area is commonly associated with telegraphic speech made up of content vocabulary. For example, a person with Broca's aphasia may say something like, "Drive, store. Mom." meaning to say, "My mom drove me to the store today." Therefore, the content of the information is correct, but the grammar and fluidity of the sentence is missing.<ref>{{Cite web | url=http://www.asha.org/PRPSpecificTopic.aspx?folderid=8589934663&section=Signs_and_Symptoms |title = Aphasia: Signs & Symptoms}}</ref>

The essential role of the Broca's area in speech production has been questioned since it can be destroyed while leaving language nearly intact. In one case of a computer engineer, a slow-growing [[glioma]] tumor was removed. The tumor and the surgery destroyed the left [[inferior frontal gyrus|inferior]] and [[middle frontal gyrus]], the head of the [[caudate nucleus]], the anterior limb of the [[internal capsule]], and the anterior [[Insular cortex|insula]]. However, there were minimal language problems three months after removal and the individual returned to his professional work. These minor problems include the inability to create syntactically complex sentences including more than two subjects, multiple causal [[Conjunction (grammar)|conjunction]]s, or [[reported speech]]. These were explained by researchers as due to [[working memory]] problems. They also attributed his lack of problems to extensive compensatory mechanisms enabled by [[neural plasticity]] in the nearby cerebral cortex and a shift of some functions to the homologous area in the right hemisphere.<ref name=pmid19274574/>