**Core Concept:** Wernicke's encephalopathy is a neurological disorder caused by thiamine deficiency, typically seen in alcoholics with malabsorption. Symptoms include confusion, ataxia, and oculomotor abnormalities. IV thiamine is the initial therapy to reverse neurological deficits.

**Why the Correct Answer is Right:** The correct answer, C, is that the first symptom to respond to IV thiamine in Wernicke's encephalopathy is confusion. Thiamine is crucial for carbohydrate and fat energy pathways, and deficiency leads to neuronal dysfunction and inflammation. IV thiamine therapy helps restore the biochemical balance and reduce inflammation, leading to symptom improvement, particularly in cognitive functions like confusion.

**Why Each Wrong Option is Incorrect:**
A. Ataxia (option A) is a late symptom in Wernicke's encephalopathy, appearing after the initial neurological deficits have progressed.
B. Oculomotor abnormalities (option B) occur later than confusion, typically after the development of ataxia.
D. Oculomotor abnormalities and confusion are the first symptoms in Wernicke's encephalopathy, not the last symptoms to respond to IV thiamine.

**Clinical Pearl:** IV thiamine therapy in Wernicke's encephalopathy is crucial for improving neurological function and preventing further neurological deterioration. Early diagnosis and treatment are essential for better outcomes, as the condition can progress to Korsakoff's syndrome and other severe complications.