Recently it has been found that the lateral intraparietal area does not command ocular responses (despite previous suggestions, e.g., Mountcastle et al. 1975), since monkeys exposed to a countermanding paradigm failed to qualify as a saccade command center (Brunamonti and Paré 2023)[1]. Moreover, the lateral intraparietal area is not necessary for the production of visually-guided saccades (Schiller and Tehovnik 2003). Furthermore, this area does not send direct projections to the saccade generator in the brain stem for the direct control of the ocular musculature [as do the frontal eye fields, for example, Schiller and Tehovnik 2015], but instead must gain access to the generator via the superior colliculus, as do all visual areas from the posterior neocortex (Schiller and Tehovnik 2015).[2] Both the frontal eye fields and the superior colliculus—which together are necessary for visually-guided saccades (Schiller et al. 1980)—send direct projections to the saccade generator in the brain stem, which permits the direct control of the saccade execution mechanism (Schiller and Tehovnik 2015). In a like manner, the frontal eye fields along with the middle temporal/middle superior temporal cortex have command and control capabilities vis-à-vis visual pursuit eye movements, since these regions send direct projections to brain stem sites critical for pursuit (Gottlieb et al. 1993, 1994; Schiller and Tehovnik 2015). Finally, it is well-accepted that the lateral intraparietal area is an association area (and not a command area), and that in humans it controls high-level mathematical computations (Friedrich and Friederici 2013; Rojas et al. 2021).[3]

As discussed, up to 50% of the neocortex in humans is dedicated to language (Sarubbo et al. 2020).[4] Given such a vital function of the neocortex, one must expect that the neurons here subserving language also exhibit command and control properties over the vocal apparatus (i.e., over the nuclei of cranial nerves: V, VII, X, and XII)and other motor centers dedicated to communication, that is, the dominant hand for writing and the movement of the eyes for reading as the head remains immobile. The M1 facial area is necessary for driving the vocal apparatus, and the hand area of M1 and the eye area of the frontal lobes, the frontal eye fields, have command over writing and reading, respectively (Penfield and Roberts 1966). The direct neuronal projections between M1 and the motor nuclei in the brain stem and spinal cord give M1 command and control over all body movements, particularly for speaking and writing (Aboitiz 2018; Penfield and Roberts 1966; Sherrington 1906; Vanderwolf 2007).[5] And for ocular responses, it is the direct neuronal projections between the frontal eye fields and the brain stem nuclei that assures maximal control over visually-guided saccadic eye movements and smooth pursuit (Schiller and Tehovnik 2015), which is central to reading (Penfield and Roberts 1966). Accordingly, the neocortex of humans has command and control over one’s vocal language, as acquired spontaneously during childhood (Chomsky 1965), and over one’s reading and writing which is acquired through schooling (Rojas et al. 2021). Interestingly, the neurons in the facial region of M1 in non-human primates do not send direct projections to the brain stem nuclei that mediate the facial/vocal musculature, therefore, forfeiting a commanding influence over the muscles required to develop language (Aboitiz 2018). Therefore, much effort was wasted on trying to train Washo, a chimpanzee, to demonstrate human-like language abilities [see: Washoe (chimpanzee) on Wikipedia, Nov, 2024].[6]

In conclusion, the evolution of human language came about once the neocortex of primates had command and control over the vocal musculature some half a million years ago (see Kimura 1993).

Footnotes:

[1] A countermanding task requires being able to regulate saccade execution and saccade inhibition. The neural activity in the lateral intraparietal area of monkeys was found not to discriminate between saccade execution and saccade cancellation and therefore it has been disqualified as a command center for ocular responses (Brunamonti and Paré 2023), which is a known property of the frontal eye fields. Also, electric currents below 10 μA is sufficient to evoke saccadic eye movements from the frontal eye fields (Bruce et al. 1986). However, to evoke such saccades systematically from other oculomotor centers within the neocortex, including the lateral intraparietal area and area V1, the behavioral state of an animal must be controlled, since an animal’s ongoing behavior can easily over-ride a stimulation-evoke response (Tehovnik and Slocum 2004). This is related to an absence of direct connectivity (or to sluggish synapses) between the neocortex and the saccade generator in the brain stem.

[2] Lesions of area V1 induces blindness and therefore abolishes most visually-driven saccadic eye movements, excepts saccades made to high-contrast visual targets a condition called blindsight (> 95% contrast, Tehovnik et al. 2021).

[3] A bar tender from Houston Texas who suffered from epilepsy: She reported to EJT that when she had seizures, whose focus was the posterior parietal cortex, that immediately after a seizure she could not perform mathematical tasks such as using her calculator to add up numbers (her ability to think in terms of numbers vanished), but her verbal abilities were fine.

[4] Semantic information is stored primarily in the neocortex where associations are made between words and objects in the form of sounds (i.e., syllables) and visual images in Wernicke’s and Broca’s areas (Kimura 1993; Ojemann 1991; Penfield and Roberts 1966), and the sound information is stored in the cerebellum in the form of syllables according to a muscle code for the generation of words using a vocal apparatus and associated muscles that can depend on up to 100 muscles for optimal performance (Simonyan and Horwitz 2011).

[5] In songbirds, the telencephalon is directly connected to the vocal nuclei in the brain stem for maximal control over singing (Schmidt and Wild 2014; Simonyan and Horwitz 2011).

[6] In the first year of study in psychology at the University of Western Ontario in the 70’s (by EJT), the investigations on Washoe were taught as being flawed experimentally, even though Washoe became an international sensation at the time.