Resting-State Connectivity in Acute and Subacute Poststroke Aphasia: A Functional Near-Infrared Spectroscopy Pilot Study

Abstract

Background: Understanding how brain function and language skills change during early (acute and subacute) stroke phases is critical for maximizing patient recovery, yet functional neuroimaging studies of early aphasia are scarce. In this pilot study, we used functional near-infrared spectroscopy (fNIRS) to investigate how resting-state functional connectivity (rs-FC) in early aphasia differs from neurologically healthy adults and is related to language deficits. Materials and Methods: Twenty individuals with aphasia (12 acute and 8 subacute phase) and 15 healthy controls underwent rs-fNIRS imaging with a 46-channel montage centered over bilateral perisylvian language areas. FC was computed using a prewhitening, autoregressive Pearson correlation routine applied to preprocessed oxyhemoglobin (HbO) data. Connections were classified as left intra-, right intra-, or interhemispheric. We then compared rs-FC between groups by connection type and examined Spearman correlations between rs-FC averages and language measures within patients. Results: Participants in the acute phase had significantly reduced global rs-FC across all HbO-based connections compared to healthy controls. No significant differences were found in rs-FC between controls and patients in the subacute phase. Controlling for days since stroke, stronger right intra- and interhemispheric rs-FC was related to milder aphasia across all patients. Exploratory correlations revealed that relationships between language measures and rs-FC differed between acute and subacute patient groups. Conclusion: This study provides preliminary evidence that fNIRS-based rs-FC measures may be a viable metric to index the early impacts of stroke in people with aphasia.

Keywords: aphasia; connectivity; functional near-infrared spectroscopy; resting state; stroke.

FIG. 1.

(A) The fNIRS montage with sources (denoted by red circles) and detectors (denoted by royal blue circles) arranged over perisylvian language regions within the left hemisphere and their right hemisphere homologues to form 46 long-distance channels (denoted by solid lines). Short distance detectors (denoted by light blue circles outlined in royal blue) formed short distance channels with four sources per hemisphere and detector 16 (sacrificed from its position in the posterior right hemisphere). (B) The sensitivity profile with the montage projected onto the brain in which warmer colors reflect higher measurement sensitivity and cooler colors indicate lower sensitivity. fNIRS, functional near-infrared spectroscopy.

FIG. 2.

Lesion overlay maps in PWA, including (A) all PWA included in the study (n = 19), (B) PWA enrolled in the study in the acute phase (n = 11), and (C) PWA enrolled in the study in the subacute phase (n = 8). The color scales indicate the maximal number of patients with lesioned tissue in a given area within each image. Note that due to a scanner software malfunction, the lesion map for PWA16 is not included in the overlay. PWA, people with aphasia.

FIG. 3.

(A) rs-FC maps within each group depict connections with significant Fisher-transformed Z values for the condition of rest, corrected at the connection level at an FDR of q < 0.05, Z range −1 to 1 in each plot. Line colors reflect the strength of connectivity, in which deeper/darker red indicates stronger positive connectivity and lighter/pinker lines indicate weaker connectivity. S, source; and D, detector. (B) Violin plots of the distribution of Fisher-transformed Z values for each connection type within each group. The solid black lines denote the mean within each group. Q < 0.01**, <0.05*, n.s., not significant after FDR correction. FDR, false discovery rate; InterHem, interhemispheric connections; IntraLH, left intrahemispheric connections; IntraRH, right intrahemispheric connections; rs-FC, resting-state functional connectivity.

FIG. 4.

Relationships between fNIRS rs-FC and overall aphasia severity and naming abilities within each patient group. BNT, Boston Naming Test; InterHem, interhemispheric connections; IntraLH, left intrahemispheric connections; IntraRH, right intrahemispheric connections; WAB-R AQ, Western Aphasia Battery-Revised Aphasia Quotient.