The Role of the Supplementary Motor Region in Overt Reading: Evidence for Differential Processing in SMA-Proper and Pre-SMA as a Function of Task Demands.

A differentiation in function between the pre-SMA (i.e., cognitive load) and the SMA-proper (i.e., motor execution) has been described (Zhang et al., Cereb Cortex 22:99-111, 2012). These differential SMA functions may be influential in overt reading tasks. The present study examined the relationships between various segments of the SMA and overt reading through the modulation of task demands in an effort to explore the complexity of the print-to-speech network. Skilled reading adults (N = 15) took part in five overt reading tasks: pure regular word reading, pure exception word reading, mixed regular word and exception word reading, go/no-go reading with nonword foils and go/no-go reading with pseudohomophone foils. Five regions of interest that spanned the pre-SMA to the SMA-proper were isolated. Behaviour-function relationships were tested to examine the associations between performance (response time) and brain activity (percent signal change). Further, the coherence between feedforward (SMA) and feedback (supramarginal gyrus) regions were explored to further refine the print-to-speech network. We found that the pre-SMA was related to cognitively demanding tasks (go/no-go with pseudohomophones), whereas the SMA-proper was related to an automatized task (pure regular words). Notably, only those tasks that required information from the feedback system (i.e., mixed word lists, go/no-go tasks) showed connections between SMA regions and the supramarginal gyrus, which is in line with the role of feedback and feedforward systems in the print-to-speech network. Together, these results support the notion that the pre-SMA and SMA-proper are sensitive to reading tasks that differentially invoke higher cognitive resources (mixed word lists, go/no-go) versus automatized articulation (pure lists), respectively. We discuss our findings in the context of print-to-speech neural networks.

A functional investigation of RAN letters, digits, and objects: how similar are they?

Although rapid automatized naming (RAN) of letters, digits, and objects are popular tasks and have been used interchangeably to predict academic performance, it remains unknown if they tap into the same neural regions. Thus, the purpose of this study was to examine the neural overlap across different RAN tasks. Fifteen university students were assessed on RAN digits, letters, and objects using functional magnetic resonance imaging (fMRI). Results showed a common neural pattern that included regions related to motor planning (e.g., cerebellum), semantic access (middle temporal gyrus), articulation (supplementary motor association, motor/pre-motor, anterior cingulate cortex), and grapheme-phoneme mapping (ventral supramarginal gyrus). However, RAN digits and letters showed many unique regions of activation over and above RAN objects particularly in semantic and articulatory regions, including precuneus, bilateral supramarginal gyrus, nucleus accumbens and thalamus. The only region unique to RAN objects included bilateral fusiform, a region commonly implicated in object processing. Overall, our results provide the first neural evidence for a stronger relationship between RAN letters and digits than when either task is compared to RAN objects.

Recent memory for socially transmitted food preferences in rats does not depend on the hippocampus.

The standard model of systems consolidation holds that the hippocampus (HPC) is involved only in the initial storage and retrieval of a memory. With time hippocampal-neocortical interactions slowly strengthen the neocortical memory, ultimately enabling retrieval of the memory without the HPC. Key support for this idea comes from experiments measuring memory recall in the socially-transmitted food preference (STFP) task in rats. HPC damage within a day or two of STFP learning can abolish recall, but similar damage five or more days after learning has no effect. We hypothesize that disruption of cellular consolidation outside the HPC could contribute to the amnesia with recent memories, perhaps playing a more important role than the loss of HPC. This view predicts that intraHPC infusion of Tetrodotoxin (TTX), which can block conduction of action potentials from the lesion sites, will block the retrograde amnesia in the STFP task. Here we confirm the previously reported retrograde amnesia with neurotoxic HPC damage within the first day after learning, but show that co-administration of TTX with the neurotoxin blocks the retrograde amnesia despite very extensive HPC damage. These results indicate that HPC damage disrupts cellular consolidation of the recent memory elsewhere; STFP memory may not ever depend on the HPC.

''Change of Mind'' within and between nonconscious (masked) and conscious (unmasked) visual processing.

We examined the updating of decisions made during visuo-motor processing when two sequentially presented stimuli, Prime1 and Prime2, primed discriminative responses to a following probe. In Experiment 1, the visibility of the two primes was suppressed or left intact by varying the stimulus onset asynchrony (SOA) of the stimuli immediately following them. In Experiment 2, the visibility of Prime2 was suppressed or left intact by varying its spatial separation from the following probe. We found (1) that Prime2 dominated the effects of Prime1; (2) that Prime2's updating was stronger when the Prime2-probe SOA was 200 as compared to 53 ms; and (3) that Prime2's updating was weaker when the Prime2-probe spatial separation was 58 as compared to 0 minarc. We conclude that these effects are due to an interaction of spatial attention and the state (conscious vs. nonconscious) of processing of Prime2.