**Core Concept**
The question targets the adverse effects of antitubercular drugs, specifically those that can cause neurological symptoms. The underlying principle is the drug's mechanism of action and its potential to cause side effects.

**Why the Correct Answer is Right**
Isoniazid (INH) is a first-line antitubercular drug that can cause peripheral neuropathy, particularly optic neuritis, and seizures. The mechanism involves the interference with pyridoxine (vitamin B6) metabolism, leading to a deficiency. This deficiency can cause neurological symptoms, including transient memory loss. INH is a prodrug that requires metabolic activation by cytochrome P450 enzymes, and its toxicity is related to the accumulation of its metabolites.

**Why Each Wrong Option is Incorrect**
**Option A:** Rifampicin is an antitubercular drug that is known for causing hepatotoxicity and gastrointestinal side effects, but it is not typically associated with transient memory loss.
**Option B:** Ethambutol can cause optic neuritis, but it is more commonly associated with visual disturbances rather than memory loss.
**Option C:** Pyrazinamide is an antitubercular drug that can cause hepatotoxicity and arthralgias, but it is not typically associated with neurological side effects like memory loss.

**Clinical Pearl / High-Yield Fact**
Isoniazid-induced neurological toxicity can be prevented by administering pyridoxine supplementation, especially in patients with a history of malnutrition or those taking other medications that interfere with vitamin B6 metabolism.

**Correct Answer:** A. Isoniazid