Hemodynamic responses in neural circuitries for detection of visual target and novelty: An event-related fMRI study

Abstract

The oddball paradigm examines attentional processes by establishing neural substrates for target detection and novelty. Event-related functional imaging enables characterization of hemodynamic changes associated with these processes. We studied 36 healthy participants (17 men) applying a visual oddball event-related design at 4 Tesla, and performed an unbiased determination of the hemodynamic response function (HRF). Targets were associated with bilateral, albeit leftward predominant changes in frontal-parietal temporal and occipital cortices, and limbic and basal ganglia regions. Activation to novelty was more posteriorly distributed, and frontal activation occurred only on the right, while robust activation was seen in occipital regions bilaterally. Overlapping regions were left thalamus, caudate and cuneus and right parietal precuneus. While robust HRFs characterized most regions, target detection was associated with a negative HRF in the right parietal precuneus and a biphasic HRF in thalamus, basal ganglia, and all occipital regions. Both height of the HRF and longer time to peak in the right cingulate were associated with slower response time. Sex differences were observed, with higher HRF peaks for novelty in men in right occipital regions, and longer time to peak in the left hemisphere. Age was associated with reduced peak HRF in left frontal region. Thus, indices of the HRF can be used to better understand the relationship between hemodynamic changes and performance and can be sensitive to individual differences.

Figure 1

Illustration of the standard, target, and novel stimuli.

Figure 2

Activation maps for the target (upper display) and novel (bottom display) conditions. Brain images showing the partial Z map are displayed in radiological convention (left is to the viewer's right). Colored areas exceed a corrected P value of 0.05.

Figure 3

The HRFs, expressed as percent change in beta coefficients from the regression based estimate of the baseline, in activated regions for the target (left two columns) and novel (right two columns). HRFs are presented separately for frontal (top raw), parietal temporal– occipital (second raw), limbic (third raw), and basal ganglia‐ thalamic regions (bottom raw). MF = Midfrontal, FPR = Frontal precentral, FPO = Frontal postcentral, IF = Inferior frontal, IP = Inferior parietal, PP = Parietal precuneus, ST = Superior temporal gyrus, LI = Lingual gyrus, CU = Cuneus, CG = Cingulate gyrus, IN = Insula, TH = Thalamus, CD = Caudate, MB = Midbrain, FG = Fusiform gyrus, MO = Mid‐occipital, PH = Parahippocampal gyrus, MT = Midtemporal.

Figure 4

Indices of the HRF for target (left column) and novel (right column) contrasts. The indices include MAX (top raw), TTF (second raw), AUCpos (third raw), and AUCneg (bottom raw). Region definitions as in Figure 3.