Language and speech depend on a relatively well defined neural circuitry, located predominantly in the left hemisphere. In this article, I discuss the origin of the speech circuit in early humans, as an expansion of an auditory-vocal articulatory network that took place after the last common ancestor with the chimpanzee. I will attempt to converge this perspective with aspects of the Mirror System Hypothesis, particularly those related to the emergence of a meaningful grammar in human communication. Basically, the strengthening of (...) auditory-vocal connectivity via the arcuate fasciculus and related tracts generated an expansion of working memory capacity for vocalizations, that was key for learning complex utterances. This process was concomitant with the development of a robust interface with visual working memory, both in the dorsal and ventral streams of auditory and visual processing. This enabled the bidirectional translation of sequential codes into hierarchical visual representations, through the development of a multimodal interface between both systems. (shrink)

We present a new road map for research on “How the Brain Got Language” that adopts an EvoDevoSocio perspective and highlights comparative neuroprimatology – the comparative study of brain, behavior and communication in extant monkeys and great apes – as providing a key grounding for hypotheses on the last common ancestor of humans and monkeys and chimpanzees and the processes which guided the evolution LCA-m → LCA-c → protohumans → H. sapiens. Such research constrains and is constrained by analysis of (...) the subsequent, primarily cultural, evolution of H. sapiens which yielded cultures involving the rich use of language. (shrink)

The meaning of the word homology has changed. From being a comparative concept in pre-Darwinian times, it became a historical concept, strictly signifying a common evolutionary origin for either anatomical structures or genes. This historical understanding of homology is not useful in classification; therefore I propose a return to its pre-Darwinian meaning.

Dysfunctions of the neural circuits that implement social behavior are necessary but not a sufficient condition to develop schizophrenia. We propose that schizophrenia represents a disease of general connectivity that impairs not only the “social brain” networks, but also different neural circuits related with higher cognitive and perceptual functions. We discuss possible mechanisms and evolutionary considerations.

We commend Arbib for his original proposal that a mirror neuron system may have participated in language origins. However, in our view he proposes a complex evolutionary scenario that could be more parsimonious. We see no necessity to propose a hand-based signing stage as ancestral to vocal communication. The prefrontal system involved in human speech may have its precursors in the monkey's inferior frontal cortical domain, which is responsive to vocalizations and is related to laryngeal control.

In early hominins, there possibly was high selective pressure for the development of reciprocal mother and child vocalizations such as proposed by Falk. In this context, temporoparietal-prefrontal networks that participate in tasks such as working memory and imitation may have been strongly selected for. These networks may have become the precursors of the future language areas of the human brain.

A functional approach to evolutionary morphology is emphasized in this paper. This perspective differs from the current structuralist trend, which emphasizes the constraining role of developmental paths. In addition, the present approach agrees with the adaptationist paradigm. It is further argued that three types of phenomena are better understood in this light: i.- the existence of evolutionary trends, ii.- the maintenance of certain structural features within a given taxon, and iii.- the irreversibility of evolution.

We present a new road map for research on “How the Brain Got Language” that adopts an EvoDevoSocio perspective and highlights comparative neuroprimatology – the comparative study of brain, behavior and communication in extant monkeys and great apes – as providing a key grounding for hypotheses on the last common ancestor of humans and monkeys and chimpanzees and the processes which guided the evolution LCA-m → LCA-c → protohumans → H. sapiens. Such research constrains and is constrained by analysis of (...) the subsequent, primarily cultural, evolution of H. sapiens which yielded cultures involving the rich use of language. (shrink)

Understanding evolution beyond a gene-centered vision is a fertile ground for new questions and approaches. However, in this systemic perspective, we take issue with the necessity of the concept of information. Through the example of brain and language evolution, we propose the autonomous systems theory as a more biologically relevant framework for the evolutionary perspective offered by Jablonka & Lamb (J&L).

A dorsalization mechanism is a good candidate for the evolutionary origin of the isocortex, producing a radial and tangential expansion of the dorsal pallium (and perhaps other structures that acquired a cortical phenotype). Evidence suggests that a large part of the dorsal ventricular ridge (DVR) of reptiles and birds derives from the embryonic ventral pallium, whereas the isocortex possibly derives mostly from the dorsal pallium. In early mammals, the development of olfactory-hippocampal associative networks may have been pivotal in facilitating the (...) selection of a larger and more complex dorsal pallium which received both collothalamic and lemnothalamic sensory information. Finally, although it is not clear exactly when mammalian brain expansion began, fossil evidence indicates that this was a late event in mammaliaform evolution. (shrink)

Finlay et al. address the importance of developmental constraints in brain size evolution. I discuss some aspects of this view such as the relation of brain size with processing capacity. In particular, I argue that in human evolution there must have been specific selection for increased processing capacity, and as a consequence for increased brain size.

In the target article, Sagvolden and collaborators propose that attentional-deficit/hyperactivity disorder (ADHD) is the result of a general behavioral deficit which is mainly caused by a hypofunctioning mesolimbic dopaminergic system. Although we partly agree with this view, we think that it tends to overlook the dysfunction of prefrontal and frontostriatal executive functions by considering them to be a consequence of alterations in reward and extinction mechanisms. Rather, we believe that ADHD is the result of an overall cognitive and behavioral condition, (...) associated to a generalized dopaminergic network dysfunction, and may not be easily attributable to a single basic behavioral function. (shrink)

By themselves, mesencephalic subcortical mechanisms provide a preattentive kind of consciousness, related to stimulus-related, short-latency dopamine release triggered by collicular input. Elaborate forms of consciousness, containing identifiable objects (visual, auditory, tactile, or chemical), imply longer-lasting phenomena that depend on the activation of prosencephalic networks. Nevertheless, the maintenance of these higher-level networks strongly depends on long-lasting mesencephalic dopamine release. (Published Online May 1 2007).

I discuss Fitch & Denenberg's argument that no correction for brain size is needed when assessing callosal size. Morphometric criteria may not be sufficient to determine whether corrections are needed. Functional studies of callosal transfer will ultimately specify whether corrections for size are necessary in each case.

While influential works since the 1970s have widely assumed that imitation is an innate skill in both human and non-human primate neonates, recent empirical studies and meta-analyses have challenged this view, indicating other forms of reward-based learning as relevant factors in the development of social behavior. The visual input translation into matching motor output that underlies imitation abilities instead seems to develop along with social interactions and sensorimotor experience during infancy and childhood. Recently, a new visual stream has been identified (...) in both human and non-human primate brains, updating the dual visual stream model. This third pathway is thought to be specialized for dynamics aspects of social perceptions such as eye-gaze, facial expression and crucially for audio-visual integration of speech. Here, we review empirical studies addressing an understudied but crucial aspect of speech and communication, namely the processing of visual orofacial cues and its integration with vocal auditory cues. Along this review, we offer new insights from our understanding of speech as the product of evolution and development of a rhythmic and multimodal organization of sensorimotor brain networks, supporting volitional motor control of the upper vocal tract and audio-visual voices-faces integration. (shrink)

The isocortex is a distinctive feature of mammalian brains, which has no clear counterpart in the cerebral hemispheres of other amniotes. This paper speculates on the evolutionary processes giving rise to the isocortex. As a first step, we intend to identify what structure may be ancestral to the isocortex in the reptilian brain. Then, it is necessary to account for the transformations (developmental, connectional, and functional) of this ancestral structure, which resulted in the origin of the isocortex. One long-held perspective (...) argues that part of the isocortex derives from the ventral pallium of reptiles, whereas another view proposes that the isocortex originated mostly from the dorsal pallium. We consider that, at this point, evidence tends to favor correspondence of the isocortex with the dorsal cortex of reptiles. In any case, the isocortex may have originated partly as a consequence of an overall “dorsalizing” effect (that is, an expansion of the territories expressing dorsal-specific genes) during pallial development. Furthermore, expansion of the dorsal pallium may have been driven by selective pressures favoring the development of associative networks between the dorsal cortex, the olfactory cortex, and the hippocampus, which participated in spatial or episodic memory in the early mammals. In this context, sensory projections that in reptiles end in the ventral pallium, are observed to terminate in the isocortex (dorsal pallium) of mammals, perhaps owing to their participation in these associative networks. Key Words: basolateral amygdala; claustrum; Emx-1; endopiriform nucleus; dorsal cortex; dorsal ventricular ridge; hippocampus; homology; olfactory cortex; Pax-6; ventral pallium. (shrink)