A rostro-caudal gradient of structured sequence processing in the left inferior frontal gyrus

Abstract

In this paper, we present two novel perspectives on the function of the left inferior frontal gyrus (LIFG). First, a structured sequence processing perspective facilitates the search for functional segregation within the LIFG and provides a way to express common aspects across cognitive domains including language, music and action. Converging evidence from functional magnetic resonance imaging and transcranial magnetic stimulation studies suggests that the LIFG is engaged in sequential processing in artificial grammar learning, independently of particular stimulus features of the elements (whether letters, syllables or shapes are used to build up sequences). The LIFG has been repeatedly linked to processing of artificial grammars across all different grammars tested, whether they include non-adjacent dependencies or mere adjacent dependencies. Second, we apply the sequence processing perspective to understand how the functional segregation of semantics, syntax and phonology in the LIFG can be integrated in the general organization of the lateral prefrontal cortex (PFC). Recently, it was proposed that the functional organization of the lateral PFC follows a rostro-caudal gradient, such that more abstract processing in cognitive control is subserved by more rostral regions of the lateral PFC. We explore the literature from the viewpoint that functional segregation within the LIFG can be embedded in a general rostro-caudal abstraction gradient in the lateral PFC. If the lateral PFC follows a rostro-caudal abstraction gradient, then this predicts that the LIFG follows the same principles, but this prediction has not yet been tested or explored in the LIFG literature. Integration might provide further insights into the functional architecture of the LIFG and the lateral PFC.

Functional Segregation of Cortical Regions Underlying Speech Timing and Articulation

“…Selective cooling of this region stretches the sequence and the resultant singing behavior (Long and Fee, 2008). Because the majority of temperature-related changes reported here also involved a decrease in speech rate, we propose the intriguing possibility that at least one affected sub-part of Broca’s region is the site of sequence generation for speech production, a notion that is consistent with some previous findings (Clerget et al, 2011; Gelfand and Bookheimer, 2003; Udden and Bahlmann, 2012). A range of relevant models can be directly addressed in future experiments using high density recording techniques to measure activity at a fine spatial scale (Bouchard et al, 2013), and even at the single neuron level (Fried et al, 2014), to better understand the nature of this local processing.…”

A rostro-caudal axis for language in the frontal lobe: The role of executive control in speech production

“…Of highest importance is the necessity to establish the functional-anatomic relationships between the various executive components of pFC and posterior primary and multisensory regions engaged in phonological perception and storage, lexical-conceptual memory and sensorimotor interface (Hickok and Poeppel, 2007), as well as other abilities often deemed 'peripheral' to language processing such as reading (Dehaene and Cohen, 2011), music (Uddén and Bahlmann, 2012) or bilingualism (Bialystok, 2009;Jeon and Friederici, 2013). In the mean time, this discussion hopefully shows the theoretical and empirical import of a comprehensive picture of the frontal lobe as the main executive component of human language.…”

Chronic ambulatory electrocorticography from human speech cortex

“…In this study, we focused on the HG band given its strong association with cortical activation (Ray et al, 2008) and relevance for linguistic neurophysiology (Leonard et al, 2016a; Leonard et al, 2016b; Steinschneider et al, 2011), though analysis of lower frequency dynamics would also be possible with data acquired by the RNS System. Future experiments employing a more diverse array of tasks could determine the specificity of the observed responses for language, motor preparation, or other aspects of cognitive processing (Udden and Bahlmann, 2012). …”