Electrophysiological Responses in the Ventral Temporal Cortex During Reading of Numerals and Calculation

Abstract

Recent evidence suggests that specific neuronal populations in the ventral temporal cortex show larger electrophysiological responses to visual numerals compared with morphologically similar stimuli. This study investigates how these responses change from simple reading of numerals to the active use of numerals in an arithmetic context. We recorded high-frequency broadband (HFB) signals, a reliable measure for local neuronal population activity, while 10 epilepsy patients implanted with subdural electrodes performed separate numeral reading and calculation tasks. We found that calculation increased activity in the posterior inferior temporal gyrus (ITG) with a factor of approximately 1.5 over the first 500 ms of calculation, whereas no such increase was noted for reading numerals without calculation or reading and judging memory statements. In a second experiment conducted in 2 of the same subjects, we show that HFB responses increase in a systematic manner when the single numerals were presented successively in a calculation context: The HFB response in the ITG, to the second and third numerals (i.e., b and c in a + b = c), was approximately 1.5 times larger than the responses to the first numeral (a). These results provide electrophysiological evidence for modulation of local neuronal population responses to visual stimuli based on increasing task demands.

Origins of the brain networks for advanced mathematics in expert mathematicians

“…Those regions included the right-hemispheric fusiform face area (FFA), bilateral parahippocampal place areas (PPAs), bilateral extrastriate body areas (EBAs), bilateral lateral occipital cortices for tools (LOCs), and left-hemispheric visual word form area (VWFA). Importantly, with high-resolution fMRI, we also found a strong number-related activation in bilateral regions of the inferior temporal gyrus, at sites corresponding to the left and right visual number form areas (VNFAs) (18,37). We also observed bilateral responses to formulas > other stimuli in both groups at bilateral sites partially overlapping the VNFA.…”

“…Bilateral intraparietal and dorsal prefrontal regions are active during a variety of number-processing and calculation tasks (16) and contain neurons tuned to numerical quantities (17). Bilateral inferior temporal regions have been termed "visual number form areas" (VNFAs) because they activate to written Arabic numerals much more than to letter strings or other pictures (18,37). The VNFAs were previously difficult to detect with fMRI because they lie close to a zone of fMRI signal loss (18).…”

Mapping human temporal and parietal neuronal population activity and functional coupling during mathematical cognition

“…Our analyses were aimed first at characterizing the response properties of subregions within the VTC and LPC to confirm the presence of numeral-and/or math-selective neuronal populations that we and other groups have reported previously (20,22,23,37,39,40). Next, we measured the relative timing of the activation of each of these regions during arithmetic computations.…”

Neuronal Population Responses in the Human Ventral Temporal and Lateral Parietal Cortex during Arithmetic Processing with Digits and Number Words

“…However, we remind the reader that the PITG occupies a relatively large extent of the VTC, and as our previous findings have suggested, there is clearly a heterogeneity of functions within this region of the brain. While a small region of the PITG (i.e., the NFA) is selectively implicated in the processing of numerals (Shum et al, 2013), a larger surrounding area of the NFA is activated during both digit and number word processing (Shum et al, 2013; Daitch et al, 2016; Hermes et al, 2017). This is in line with the findings that the area lateral to the NFA, i.e., the Visual Word Form Area (VWFA) (Nobre et al, 1994; Cohen et al, 2000), is involved in processing word form symbols.…”

“…Corroborating Triple Code model’s hypothesized role of VTC, we recently found a small site within the posterior inferior temporal gyrus (PITG) in the VTC that respond selectively to visual numerals compared to number words and stimuli morphologically similar to numerals such as letters and false fonts (‘Number form area’ or ‘NFA’) (Shum et al, 2013). We later discovered that a larger region of the PITG, including and surrounding the NFA, becomes engaged during active arithmetic processing (Hermes et al, 2017), and interacts dynamically with the IPS region during not only arithmetic processing but also during the resting state (Daitch et al, 2016). …”