Schematic diagram of the left hemisphere depicting Broca’s Wernicke’s areas, the angular gyrus, Exner’s (Ex) writing area, the frontal eye fields (FEF), and the orbital frontal lobe (OF). Heavy lines indicate arcuate fasciculus pathways. (From Joseph, 1982.) 

Context in source publication

Context 1

... This condition is referred to as apraxia, i.e., an inability to perform tasks involving interrelated steps and sequences (De Renzi and Lucchetti, 1988; Geschwind, 1965; Joseph, 1990; Heilman et al ., 1982; Kimura, 1993). With severe IPL injuries, the individual may be unable to make a cup of coffee or put on clothes, much less fashion or sew them together. Moreover, grammatical speech is disrupted and patients may suffer extreme word finding difficulty, or a conduction aphasia. That is, speech is no longer produced, as Broca’s area is disconnected from the IPL and Wernicke’s area (Geschwind, 1965; Joseph, 1990, 1993). Likewise, reading ability is disrupted, as the IPL comprehends and produces not only gestures but visual symbols including written language. Hence, the IPL/angular gyrus (including the frontal motor areas) makes possible the ability to fashion and manipulate tools and organizes speech into vocabulary-rich, temporal sequential grammatical units. As apes do not possess an angular gyrus (Geschwind, 1965), it appears that over the course of evolution, with the development of right-handedness and selec- tive pressures acting on gene selection across gathering/toolmaking generations, the IPL/angular gyrus emerged as an extension of the auditory area in the temporal lobe and the superior parietal visual–hand area. Indeed, the parietal lobes are considered a “lobe of the hand” and contain neurons which guide hand movements (Hyvarinen, 1982; Kaas, 1993; Lynch, 1980; Mountcastle et al ., 1975, 1980) and which respond to visual input from the periphery and lower visual fields—the regions in which toolmaking hands are most likely to come into view (Joseph, 1993, 2000). Because most individuals would use the right hand for toolmaking and the left for holding the tool, it is the left parietal lobe (which monitors the right lower visual field and controls the right hand) that guides and visually observes, learns, and memorizes hand movements when gathering, gesturing, or manipulating some object or constructing a tool (Joseph, 2000). Over the course of evolution and as experience and the environment act on gene selection and induce neural plasticity (e.g., Joseph, 1999b, 2000), the parietal (and superior temporal) lobe expanded, the angular gyrus emerged, and neuroplastic alterations were induced in the adjoining motor–hand area in the frontal lobe including what would become Broca’s speech area. The angular gyrus sits at the junction of the posterior–superior temporal and the occipital–parietal lobes, and is critically involved in naming, word finding, and grammatical speech organization, and is in part an extension of and links Wernicke’s with Broca’s area (Joseph, 1982, 1988, 1990; Geschwind, 1965; Goodglass and Kaplan, 2000; Kimura, 1993). Through its extensive interconnec- tions with the adjacent sensory association areas, the IPL/angular gyrus receives and assimilates complex associations, thereby forming multimodal concepts, and acts to classify and name this material, which is then injected into the stream of language and thought (Joseph, 1982, 1990). The IPL/angular gyrus, in concert with Wernicke’s area, transmits this information to Broca’s speech area, which in turn organizes the immediately adacent oral, laryngeal motor areas (Foerster, 1936; Fox, 1995; Joseph, 1990). However, primates only lack not an angular gyrus, but a functional Broca’s area. Among nonhuman primates, the left frontal lobe, including the tissues homologous to Broca’s area, does not subserve speech or vocalization (Jurgens et al ., 1982; Myers, 1976). Rather, vocalization in primates and other nonhuman mammals is the province of the limbic system and brain stem, e.g., the cingulate gyrus, amygdala, hypothalamus, and periaqueductal gray (Joseph, 1992, 1996b; Jurgens, 1990; MacLean, 1990; Robinson, 1967, 1972), and has a nonsegmented organization, consisting of moans, screams, barks, grunts, pants, and pant-hoots (Erwin, 1975; Fedigan, 1992; Goodall, 1986, 1990; Hauser, 1997). Thus, although dam- age to Broca’s area in humans results in a profound expressive aphasia, similar destruction in nonhuman primates has no effect on vocalization rate, the acousti- cal structure of primate calls, or social–emotional communication (Jurgens et al ., 1982; Myers, 1976). Rather, in primates, “Broca’s area” is directly involved in manual activity (Rizzolatti et al ., 1988), and the neural pathways linking the primate IPL with the homologous primate “Broca’s area” are only weakly developed (Abolitiz and Garcia, 1997). In contrast, 90% of primate auditory cortex neurons are activated by species- specific calls (Newman and Wollberg, 1973), whereas destruction of the left superior temporal lobe disrupts that ability to make sound discriminations (Heffner and Heffner, 1984; Hupfer et al ., 1977; Schwarz and Tomlinson, 1990). Moreover, asymmetries in the planum temporal are apparent in chimpanzees (Gannon, 1998), and the primate left hemisphere (Fig. 6) has also been shown to be dominant for the perception of primate vocalizations (Hauser and Anderson, 1994; Peterson and Jusczyk, 1984; Peterson et al ., 1978). Presumably, left planum temporal and hemisphere dominance for vocal perception and comprehension gradually increased in the transition from Australopithecus , to H. habilis , to H. erectus , to Neanderthals. As first proposed and detailed elsewhere (Joseph, 1993, 1996a,b), as Wernicke’s area, the parietal–hand areas and the IPL expanded, merged, and collectively gave rise to the angular gyrus, auditory input began to be sequenced, and Wernicke’s area became specialized to perceive and comprehend language units. In addition, the arcuate fasciculus axonal pathways leading from the IPL to Broca’s areas also significantly expanded and increased in density, and Wernicke’s area became tightly linked with and began transmitting auditory–linguistic signals to Broca’s area, thus inducing neurplas- tic alterations in these tissues (for related discussion see, e.g., Joseph, 1999b– d). Hence, Wernicke’s area began sequencing auditory input, and Broca’s area was transformed from a hand area to a speech area and ceased to control hand movements. Instead Broca’s area began to organize the adjacent primary motor oral–laryngeal areas so as to express the words and sentences transmitted from the IPL and Wernicke’s area. Moreover, as the right and left frontal vocalization areas are richly interconnected with the anterior cingulate vocalization centers, whereas the temporal lobe is tightly linked with the amygdala, once these neural–plastic transformations took place, “limbic language” (emotional speech) became hierarchically represented, yoked to the neocortex, and subject to fractionization, temporal sequencing, and multiclassification. Wernicke’s area was now able to communicate with Broca’s area, with the angular gyrus injecting temporal sequences and assimilated associations into the stream of language and thought. Hence, in addition to manipulating tools in a temporal sequential fashion, the evolution of the IPL/angular gyrus enabled humans to manipulate the internal environment and to transmit linguistic impulses to the frontal motor areas controlling the oral– laryngeal musculature, thereby reorganizing Broca’s area in order to vocalize units of speech. However, as based on an analysis of tool technology, it can be concluded that Australopithecus , H. habilis , H. erectus , and Neanderthals did not possess the neurological sophistication for vocalizing complex human language and had not yet evolved an angular gyrus or a functional Broca’s area (Joseph, 1996a). Rather, the evolution of modern speech likely corresponded to the evolution of the Upper Paleolithic female gatherer and toolmaker. The frontal motor area representing the hand is immediately adjacent to and intimately interconnected with the primary motor areas mediating oral, laryngeal, and mandibular movements, including Broca’s area (Fox, 1995; Joseph, 1982, 1988). Hence, manual activity, right-handedness, and expressive speech are directly related (Bradshaw and Rogers, 1992; Corbalis, 1991; Hicks, 1975; Joseph, 1982; Kimura, 1993; Kinsbourne and Cook, 1971), which is why, when speaking, humans commonly gesture with the hands, the right hand in particular. However, it was not until the late Middle Paleolithic that up to 90% of Paleolithic humans may have become right-handed (Cornford, 1986). Similarly, it was not until the Middle to Upper Paleolithic transition, 35,000 years ago, that toolmaking became literally an art and complex multifaceted features were incorporated in their construction and utilization (Chauvet et al ., 1996; Joseph, 1993, 1996a; Leroi-Gourhan, 1964, 1982; Mellars, 1989). The Middle/Upper Paleolithic transition is characterized by the creation of complex bone tools, the sewing needle, and personal adornments such as carefully shaped beads of bone, ivory and animal teeth, animal engravings, perforated shells, statuettes, drawings, and paintings of animal and female figures (Chauvet et al ., 1996; Clark, 1967; Leroi-Gourhan, 1964, 1982; Mellars, 1989). As the creation and wearing of personal adornments and domestic tool construction and use are associated with the human female, and as toolmaking and gathering often involve both hands (albeit the right more than the left), it might be expected that the human female frontal–parietal areas may have functionally evolved in a manner different from men. That is, both the left and the right half of the female brain may have become organized for producing motor sequences and grammatically complex vocabulary-rich speech. Moreover, as the parietal lobe and IPL/angular gyrus act on and program the frontal motor and speech areas (De Renzi and Lucchetti 1988; Heilman et al ., 1982; Kimura, 1993; Strub and Geschwind, 1983), it might be expected that sex differences would be more pronounced in Broca’s and the parietal areas. In ...