Words in the brain's language

Abstract

If the cortex is an associative memory, strongly connected cell assemblies will form when neurons in different cortical areas are frequently active at the same time. The cortical distributions of these assemblies must be a consequence of where in the cortex correlated neuronal activity occurred during learning. An assembly can be considered a functional unit exhibiting activity states such as full activation (“ignition”) after appropriate sensory stimulation (possibly related to perception) and continuous reverberation of excitation within the assembly (a putative memory process). This has implications for cortical topographies and activity dynamics of cell assemblies forming during language acquisition, in particular for those representing words. Cortical topographies of assemblies should be related to aspects of the meaning of the words they represent, and physiological signs of cell assembly ignition should be followed by possible indicators of reverberation. The following postulates are discussed in detail: (1) assemblies representing phonological word forms are strongly lateralized and distributed over perisylvian cortices; (2) assemblies representing highly abstract words such as grammatical function words are also strongly lateralized and restricted to these perisylvian regions; (3) assemblies representing concrete content words include additional neurons in both hemispheres; (4) assemblies representing words referring to visual stimuli include neurons in visual cortices; and (5) assemblies representing words referring to actions include neurons in motor cortices. Two main sources of evidence are used to evaluate these proposals: (a) imaging studies focusing on localizing word processing in the brain, based on stimulus-triggered event-related potentials (ERPs), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI), and (b) studies of the temporal dynamics of fast activity changes in the brain, as revealed by high-frequency responses recorded in the electroencephalogram (EEG) and magnetoencephalogram (MEG). These data provide evidence for processing differences between words and matched meaningless pseudowords, and between word classes, such as concrete content and abstract function words, and words evoking visual or motor associations. There is evidence for early word class-specific spreading of neuronal activity and for equally specific high-frequency responses occurring later. These results support a neurobiological model of language in the Hebbian tradition. Competing large-scale neuronal theories of language are discussed in light of the data summarized. Neurobiological perspectives on the problem of serial order of words in syntactic strings are considered in closing.

Grammatical processing of nouns and verbs in left frontal cortex?

“…However, the significance of this association has been controversial. Citing its proximity to neural circuits known to subserve motor planning, some researchers have proposed that the left prefrontal cortex is activated during the retrieval of action words [43,54], not of verbs as such. Others have noted that left frontal evoked potentials are observed in response to non-action verbs as well as action verbs [16], and a recent study using repetitive transcranial magnetic stimulation (rTMS) showed that suppression of the left prefrontal cortex in normal subjects induces selective delays in responses to verb and pseudo-verb processing tasks very similar to the ones used here [50].…”

“…Some patients are poor at naming verbs relative to nouns [4,6,9,33,35], while others are worse at naming nouns than verbs [2,35,47,56]. But these deficits have most often been interpreted as resulting from damage to sensorimotor networks that store or mediate access to conceptual knowledge about objects and actions [12,43,54]. By contrast, relatively little discussion has focused on the possibility that they reflect the loss of neural representations of nouns and verbs as morphological types [9,50,51], and no attempt has been made to characterize such putative representations at the level of cortical function, in spite of the crucial role that grammatical category information plays in language processing.…”

Comparing Electrophysiological Correlates of Word Production in Immediate and Delayed Naming Through the Analysis of Word Age of Acquisition Effects

“…For instance, metalinguistic tasks associated to go/no go paradigms have been largely used since the first ERP studies on speech production with healthy subjects (Jescheniak, Schriefers, Garrett, & Friederici, 2002;Rodriguez-Fornells, Schmitt, Kutas, & Münte, 2002;Schmitt, Münte, & Kutas, 2000;Van Turennout, Hagoort, & Brown, 1998, 1999Zhang & Damian, 2009) and with brain damaged (aphasic) speakers Hensel, Rockstroch, Berg, & Schonle, 2004). Besides the drawback of using a metalinguistic task to study speech production, the interpretation of such results in terms of time-course of the addressed encoding processes is problematic.…”

“…Lexical frequency was a strong predictor of word production latencies in many studies using word reading (e.g., Gerhand & Barry, 1998;1999see Andrews & Heathcote, 2001 for a review) or picture naming tasks (e.g., Bonin, Fayol & Gombert, 1998;Jescheniak & Levelt, 1994;Oldfield & Wingfield, 1965). However, the reliably of lexical frequency effects has been challenged since effects of word AoA have also been reported (e.g., Bonin, Fayol, & Chalard, 2001;Bonin, Chalard, Méot, & Fayol, 2002;Chalard, Bonin, Méot, Boyer, & Fayol, 2003;Morrison, Ellis, & Quinlam, 1992;Morrison & Ellis, 1995).…”

Intentional action: from anticipation to goal-directed behavior

“…For example, goal representations have a crucial role in the planning and control of action, and action understanding and imitation are performed at the goal rather than at the movement level (Iacoboni et al, 2005;Wohlschläger, Gattis,& Bekkering, 2003). Moreover, it has been shown that these apparently unrelated abilities and others which were believed to be in the realm of abstract thought, such as language understanding, share common representational structures and mechanisms in the brain and involve signiWcant use of the motor system (Fadiga, Craighero, Buccino, & Rizzolatti, 2002;Pulvermüller, 1999). Recent studies have revealed the crucial role of canonical and mirror neurons (Rizzolatti & Craighero, 2004;Rizzolatti et al, 1988) and internal forward models (Kawato, 1999;Wolpert & Ghahramani, 2004) in most of the aforementioned tasks.…”