Limbique is a neuroscientific visualization project in the form of a sculptural installation. We begin by using magnetic resonance imaging (MRI) to acquire a high-resolution (1 cubic mm) brain image. This image is then decomposed into multiple 2-Dimensional coronal ‘slices’ that serve as templates for vector graphics outlining the cortex (outer surface), the white matter/gray matter boundary (inner tracing), and the specific regions of interest. Next, these vector based images are used to create high-precision acrylic renderings of each brain slice and anatomical region of interest. Finally, the acrylic pieces are assembled and suspended according to their relative positions in brain-space. Our motivation is to bring to awareness some of the lesser known but critically important components of the brain that belong to the constellation of structures known historically as le grande lobe limbique, a.k.a the limbic system. Occluded by the often more voluminous and characteristic gray matter of the cortical surface, these components are situated deep in the brain. Although they may differ in size and shape across species, they are common to mammals, birds, and reptiles. Without these basic components, practically every aspect of our function would suffer. Thus, in addition residing at the center of our brains, limbique is also positioned at the center of our lives.
The current study investigated the neural activity patterns associated with numerical sensitivity in adults. Event-related potentials (ERPs) were recorded while adults made same/different judgments comparing the numerosity of sequentially presented display arrays (S1 and S2) of non-symbolic numerical stimuli (dots). The main goals were to contrast the effects of numerical distance (close, medium, and far) and change direction (increasing, decreasing) between S1 and S2, both in terms of behavior and brain activity, and to examine the influence of individual differences in numeracy on the effects of these manipulations. Distance effects were found to be significant between 360-600 ms after the onset of S2 (greater negativity-wave activity for closer numerical distances), while direction effects were found between 320-440ms (greater negativity for decreasing direction). ERP change-direction effects did not interact with numerical distance, suggesting that the two types of information are processed independently. Importantly, subjects’ behavioral Weber fractions (w) for the same/different discrimination task were correlated with distance-related ERP activity amplitudes. Moreover, w also correlated with a separate objective measure of mathematical ability. Results thus draw a clear link between brain and behavior measures of number discrimination, while also providing support for the relationship between non-verbal magnitude discrimination and symbolic numerical processing.
Previous research has shown that, in the context of event-related potential (ERP) prime-target experiments, processing meaningful stimuli such as words, phonemes, numbers, pictures of objects, and faces elicit negativities around 400 milliseconds. However, there is little information on whether non-symbolic numerical magnitudes elicit this negative component. The present experiments recorded ERPs while adults made same/different judgments to serially presented prime-target pairs of non-symbolic numerical stimuli containing the same, close, or distant quantities. In Experiment 1, a negativity between 350-450 ms was elicited for targets preceded by primes of unequal quantity, and this was greater for close than for distant quantities. Change direction (decreasing or increasing) also modulated a similar negativity: a greater negativity was elicited by targets preceded by larger than by smaller quantities. Experiment 2 replicated the numerical distance and change direction effects for numerical judgments, but found no negative distance effect in a color comparison task when the same stimuli were used. Additionally, ERP effects of numerical distance were found under implicit conditions, and task proficiency in the number condition modulated implicit and explicit numerical distance ERP effects. These results suggest that the neural systems involved with processing numerical magnitudes contribute to the construction of meaningful, contextual representations, are partly automatic, and display marked individual differences.
